Is there any way apart from using key vault, agentless pipeline and parameters to provide user input during pipeline runtime in azure?

Since Azure Pipelines are non-interactive, there is no way out-of-the-box to input variable values during a pipeline run.

While inspired by @ScottRichards insightful answer, you may consider using the workaround below to update the values of the variables from pipelines library (variable group) during the process of a running pipeline.

Here is a simple YAML pipeline to use a variable group (in the job scope).

stages:
- stage: StageA
  jobs:
  - job: Job1
    variables:
    - group: VG-Job
    steps:
    - script: echo $(Var1)

  - job: Job2
    dependsOn: Job1
    variables:
    - group: VG-Job
    steps:
    - script: echo $(Var1)

1. Setup the variable group with the name VG-Job; in the variable group, add a variable $(Var1) with the original value ValueXXXXX;
   
2. Enable Approvals check for this variable group;
   
   
3. When running the pipeline, it will suspend the execution of StageA to wait for the approval by the approver to use the variable group resource VG-Job;
   
4. Before approval, the approver may update the value of the variable $(Var1) in this variable group and proceed to approve and resume the pipeline stage;
   
5. The output value of the variable $(Var1) during the pipeline run will be the updated value ValueYYYYY rather than its original value ValueXXXXX, since the value of a variable in a variable group is processed at runtime;
   

Kindly be also advised that,

Checks are a mechanism available to the resource owner to control if and when a stage in a pipeline can consume a resource (like variable group in our case). As an owner of a resource, such as an environment (variable group), you can define checks that must be satisfied before a stage consuming that resource can start.

This is to say for Job2 in the same stage as that of Job1, it will not suspend the pipeline again to ask for approval.

Hope the workaround may help resolve your queries.