Flutter android app fails upon launch after kotlin version upgrade, what could be the issue?

I’ve had a flutter project I’ve run on iOS and Android with no issues for the past month. Recently I finished development and build a release version that I had to upgrade kotlin for, all good. However I tried to make some final changes and run on debug again to check compatibility and the app closes as soon as it launches.

I have experience with iOS but I’m absolutely lost on what to do with Android Studio.

• Downgrade java to 17?
• Upgrade Gradle to 8.5? (which supports java 21?)
• Some configuration error in my project?

There have been other questions very similar to this about version 63 and 61 but I haven’t been able to resolve this with the advice from those questions.

$ flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.19.3, on macOS 14.4.1 23E224 darwin-arm64, locale en-AU)
[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2023.2)
[✓] VS Code (version 1.89.0)
[✓] Connected device (5 available)
[✓] Network resources

$ java --version

OpenJDK 64-Bit Server VM Homebrew (build 21.0.2, mixed mode, sharing)

$ ./gradlew clean -scan

Task :gradle:compileGroovy FAILED

FAILURE: Build failed with an exception.

* What went wrong:
  Execution failed for task ':gradle:compileGroovy'.
 BUG! exception in phase 'semantic analysis' in source unit '/Users/myName/Applications/Flutter/flutter/packages/flutter_tools/gradle/src/main/groovy/app_plugin_loader.groovy' 
Unsupported class file major version 65

So it looks like I’m using Java 21 which is not supported by my project build files?

The only changes I made to build the release version of my app was change the kotlin version from 1.7.10 >> 1.9.24.

Since then I’ve upgraded Gradle from 7.3 >> 7.6.1

Here’s my flutter android config files:

gradle-wrapper.properties

distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
distributionUrl=https://services.gradle.org/distributions/gradle-7.6.1-bin.zip
networkTimeout=10000
validateDistributionUrl=true
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists

settings.gradle

pluginManagement {
    def flutterSdkPath = {
        def properties = new Properties()
        file("local.properties").withInputStream { properties.load(it) }
        def flutterSdkPath = properties.getProperty("flutter.sdk")
        assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
        return flutterSdkPath
    }
    settings.ext.flutterSdkPath = flutterSdkPath()

    includeBuild("${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle")

    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}

plugins {
    id "dev.flutter.flutter-plugin-loader" version "1.0.0"
    id "com.android.application" version '7.4.2' apply false
    // START: FlutterFire Configuration
    id "com.google.gms.google-services" version "4.3.15" apply false
    id "com.google.firebase.crashlytics" version "2.8.1" apply false
    // END: FlutterFire Configuration
    id "org.jetbrains.kotlin.android" version "1.9.24" apply false // was 1.7.10
}

build.gradle (app-level)

...

android {
    namespace "..."
    compileSdk flutter.compileSdkVersion
    ndkVersion flutter.ndkVersion

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    kotlinOptions {
        jvmTarget = '1.8'
    }

    sourceSets {
        main.java.srcDirs += 'src/main/kotlin'
    }

    defaultConfig {
        applicationId "..."
        minSdkVersion flutter.minSdkVersion
        targetSdkVersion flutter.targetSdkVersion
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }

    // Load signing information
    signingConfigs {
       release { ... }
   }

    buildTypes {
        debug {
            signingConfig signingConfigs.debug
        }
        release {
            signingConfig signingConfigs.release
        }
    }
}

flutter { ... }

dependencies { ... }

Any ideas? Thank you

I’ve tried

• flutter clean, flutter pub get, flutter run
• Deleted app from device
• Restarted emulator
• Upgrade Gradle to a later version 7.6
• Modified gradel-wrapper.properties to include new gradle version
• Downgraded kotlin (upgraded again as this doesn’t work)