How do I overcome MissingMethodException please. Am running out of ideas – Asp.net

Have a Solution with 2 Projects, Report and Web developed in .net core 2.1 using AlanJudenMvcReportViewer which is working ok on about a dozen SSRS server reports.
Decided to use Microsoft.DotNet.UpgradeAssistant to migrate to net 5.0. Struck many errors which I have overcome with the exception of this one:

Running any report in net 5.0 now gives me ‘Report failed to load, check report parameters’ which is actually a 500 / internal server error:
System.MissingMethodException: Method not found: ‘Microsoft.AspNetCore.Mvc.JsonResult Microsoft.AspNetCore.Mvc.Controller.Json(System.Object, Newtonsoft.Json.JsonSerializerSettings)’.

The error is occuring in ReportViewer.cshtml/viewReportPage at : $.get("/Report/ViewReportPage/[email protected]()&page=" + page + "&" + urlParams)

Some research gave me: https://github.com/alanjuden/MvcReportViewer/issues/92 (and others):

… There are two solutions, one involves modifying the ReportController from Alan’s code, and the other involves including a package reference and modifying your startup to instruct MVC to use Newtonsoft JSON.

Option #1: In MvcReportViewer/ReportController/ViewReportPage method, completely replace the following code

new Newtonsoft.Json.JsonSerializerSettings() { ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver() });

with… new System.Text.Json.JsonSerializerOptions());

Option #2: First add a package reference to your .csproj file for your project in the ItemGroup that contains your other package references…

Then, in your Startup.cs/ConfigureServices method, instruct MVC to use Newtonsoft JSON… services.AddMvc().AddNewtonsoftJson();….

Have tried Option #2 – no change, same error.
Dont know how to apply Option #1 as I dont see the code to replace (and that may be the problem).

Have seen reference to problems with using earlier version packages.As far as I can see I have updated all of mine.

The ReportController.cs I am using is :

using System.Net;
using Microsoft.AspNetCore.Mvc;
using SSFA_Web.Models;
using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Authorization;

namespace SSFA_Web.Controllers
{
    [Authorize]
    public class ReportController : AlanJuden.MvcReportViewer.ReportController 
      {
        private readonly SSFA_SQLContext _context;

        public ReportController(SSFA_SQLContext context)
        {
            _context = context;
        }

        protected override ICredentials NetworkCredentials 
        { 
            get 
            {
                return new System.Net.NetworkCredential("Myusername", "Mypassword", "Mydomain"); 
            }
        }

        protected override System.ServiceModel.HttpClientCredentialType ClientCredentialType
        {
            get
            {
                return System.ServiceModel.HttpClientCredentialType.Ntlm;
            }
        }

        protected override string ReportServerUrl
        { 
            get 
            {
                return "http://MyReportServer directory"; 
            } 
        }

        protected override bool UseCustomReportImagePath { get { return true; } }

        protected override string ReportImagePath
        { 
            get 
            { 
                return "/Report/ReportImage/?originalPath={0}";
            } 
        }
                
        
        public ActionResult CalendarListing()
        {
            var model = this.GetReportViewerModel(Request);
            model.ReportPath = "/Reports/CalendarListing";
            
            return View("ReportViewer", model);
        }

    // etc
        
    }
}

The ReportViewer.cshtml is :

@model AlanJuden.MvcReportViewer.ReportViewerModel
@using AlanJuden.MvcReportViewer

@{
    ViewBag.Title = "ReportViewer";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>ReportViewer</h2>

@section AdditionalHeadContent {
    <link rel="stylesheet" href="~/lib/bootstrap/dist/css/bootstrap.css" />
    <link rel="stylesheet" href="~/lib/bootstrap/dist/css/select2.min.css" />
    <link rel="stylesheet" href="~/lib/bootstrap/dist/css/select2-bootstrap.min.css" />
    <link rel="stylesheet" href="~/lib/bootstrap/dist/css/mvcreportviewer-bootstrap.css" />
    <style>
        .row {
            margin-left: 0;
            margin-right: 0;
        }
    </style>
    <script src="~/lib/bootstrap/dist/js/select2.min.4.0.3.js"></script>
    <script src="~/lib/jquery/dist/jquery.highlight-5.js"></script>
    <script>
            $(document).ready(function () {
                _initializeReportViewerControls();

                $('.FirstPage, .ViewReport, .Refresh').click(function () {
                    if (!$(this).attr('disabled')) {
                        viewReportPage(1);
                    }
                });

                $('.PreviousPage').click(function () {
                    if (!$(this).attr('disabled')) {
                        var page = parseInt($('#ReportViewerCurrentPage').val()) - 1;

                        viewReportPage(page);
                    }
                });

                $('.NextPage').click(function () {
                    if (!$(this).attr('disabled')) {
                        var page = parseInt($('#ReportViewerCurrentPage').val()) + 1;

                        viewReportPage(page);
                    }
                });

                $('.LastPage').click(function () {
                    if (!$(this).attr('disabled')) {
                        var page = parseInt($('#ReportViewerTotalPages').text());

                        viewReportPage(page);
                    }
                });

                $('#ReportViewerCurrentPage').change(function () {
                    var page = $(this).val();

                    viewReportPage(page);
                });

                $('.ExportXml, .ExportCsv, .ExportPdf, .ExportMhtml, .ExportExcelOpenXml, .ExportTiff, .ExportWordOpenXml').click(function () {
                    exportReport($(this));
                });

                $('#ReportViewerSearchText').on("keypress", function (e) {
                    if (e.keyCode == 13) {
                        // Cancel the default action on keypress event
                        e.preventDefault();
                        findText();
                    }
                });

                $('.FindTextButton').click(function () {
                    findText();
                });

                $('.Print').click(function () {
                    printReport();
                });
            });

            function _initializeReportViewerControls() {
                $('select').select2();

                try {
                    ReportViewer_Register_OnChanges();
                } catch (e) { }
            }

            function reloadParameters() {
                var params = $('.ParametersContainer :input').serializeArray();
                var urlParams = $.param(params);

                showLoadingProgress("Updating Parameters...");

                $.get("/Report/ReloadParameters/[email protected]()&" + urlParams).done(function (data) {
                    if (data != null) {
                        $('.Parameters').html(data);
                        _initializeReportViewerControls();

                        if ($('.ReportViewerContent').find('div').length != 1) {
                            $('.ReportViewerContent').html('<div class="ReportViewerInformation">Please fill parameters and run the report...</div>');
                        }
                    }
                    hideLoadingProgress();
                });
            }

            function showLoadingProgress(message) {
                hideLoadingProgress();

                $('.ReportViewerContent').hide();
                $('.ReportViewerContentContainer').append('<div class="loadingContainer"><div style="margin: 0 auto; width: 100%; text-align: center; vertical-align: middle;"><h2><i class="glyphicon glyphicon-refresh gly-spin"></i>' + message + '</h2></div></div>');
            }

            function hideLoadingProgress() {
                $('.loadingContainer').remove();
                $('.ReportViewerContent').show();
            }

            function printReport() {
                var params = $('.ParametersContainer :input').serializeArray();
                var urlParams = $.param(params);

                window.open("/Report/PrintReport/[email protected]()&" + urlParams, "_blank");
            }

            function findText() {
                $('.ReportViewerContent').removeHighlight();
                var searchText = $("#ReportViewerSearchText").val();
                if (searchText != undefined && searchText != null && searchText != "") {
                    showLoadingProgress('Searching Report...');
                    var params = $('.ParametersContainer :input').serializeArray();
                    var urlParams = $.param(params);

                    var page = parseInt($('#ReportViewerCurrentPage').val());

                    $.get("/Report/FindStringInReport/[email protected]()&page=" + page + "&searchText=" + searchText + "&" + urlParams).done(function (data) {
                        if (data > 0) {
                            viewReportPage(data, function () {
                                $('.ReportViewerContent').highlight(searchText);
                                hideLoadingProgress();
                            });
                        } else {
                            $('.ReportViewerContent').highlight(searchText, { wholeWord: false, ignoreCase: true, color: "#ffff00", bold: true });
                            hideLoadingProgress();
                        }
                    });
                }
            }

            function viewReportPage(page, afterReportLoadedCallback) {
                showLoadingProgress('Loading Report Page...');
                var params = $('.ParametersContainer :input').serializeArray();
                var urlParams = $.param(params);
                var totalPages = parseInt($('#ReportViewerTotalPages').text());

                if (page == undefined || page == null || page < 1) {
                    page = 1;
                } else if (page > totalPages) {
                    page = totalPages;
                }

                $.get("/Report/ViewReportPage/[email protected]()&page=" + page + "&" + urlParams)
                    .done(function (data) {
                        updateReportContent(data);
                        hideLoadingProgress();

                        if (afterReportLoadedCallback && typeof (afterReportLoadedCallback) == "function") {
                            afterReportLoadedCallback();
                        }
                })
                    .fail(function (data) {
                        $('.ReportViewerContent').html("<div class='ReportViewerError'>Report failed to load, check report parameters...</div>");
                        hideLoadingProgress();
                });
            }

            function exportReport(element) {
                var params = $('.ParametersContainer :input').serializeArray();
                var urlParams = $.param(params);
                var format = $(element).attr('class').replace("Export", "");

                window.location.href = "/Report/ExportReport/[email protected]()&format=" + format + "&" + urlParams;
            }

            function updateReportContent(data) {
                if (data != undefined && data != null) {
                    $('#ReportViewerCurrentPage').val(data.CurrentPage);
                    $('#ReportViewerTotalPages').text(data.TotalPages);
                    $('.ReportViewerContent').html($.parseHTML(data.Content));

                    if (data.TotalPages <= 1) {
                        $('.FirstPage').attr('disabled', true);
                        $('.PreviousPage').attr('disabled', true);
                        $('.NextPage').attr('disabled', true);
                        $('.LastPage').attr('disabled', true);
                    } else {
                        $('.FirstPage').attr('disabled', false);
                        $('.PreviousPage').attr('disabled', false);
                        $('.NextPage').attr('disabled', false);
                        $('.LastPage').attr('disabled', false);
                    }
                }
            }
    </script>
}

@section Content {
    @Html.RenderReportViewer(Model)
}

Any help would be appreciated.