[Flutter] Unknown Kotlin JVM Target: 21 - Flutter Build Error in Beginner Project

I'm a beginner in Flutter app development and I'm encountering an error while trying to build an APK using flutter build apk. The error message mentions an "Unknown Kotlin JVM target: 21" within the nb_utils module.

Here's what I've tried so far:

I've changed my Java SDK version to Java 11. The full error message is:

FAILURE: Build failed with an exception.

• What went wrong: Could not determine the dependencies of task ':nb_utils:compileReleaseKotlin'.

Unknown Kotlin JVM target: 21
​

• Try:

Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights. Get more help at https://help.gradle.org.
​

BUILD FAILED in 1s Running Gradle task 'assembleRelease'... 1,620ms Gradle task assembleRelease failed with exit code 1

my build.gradle

plugins {
id "com.android.application"
id "kotlin-android"
id "dev.flutter.flutter-gradle-plugin"
id "com.google.gms.google-services"
}

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
localPropertiesFile.withReader('UTF-8') { reader ->
localProperties.load(reader)
}
}

android {
compileSdkVersion 34

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

lintOptions {
disable 'InvalidPackage'
}

defaultConfig {
applicationId "com.mighty.web"
minSdkVersion 22
targetSdkVersion 34
versionCode 36
versionName "5.0.2"
multiDexEnabled true
}

buildTypes {
release {
minifyEnabled false
shrinkResources false
signingConfig signingConfigs.debug
}
}

googleServices { disableVersionCheck = true }

}

flutter {
source '../..'
}
allprojects {
/// TODO: remove. hotfix for flutter_inappwebview (using androidx.webkit:webkit:1.8.0)
/// webview_flutter_android: ^3.16.2 androidx.webkit:webkit ^1.9.0 remove SUPPRESS_ERROR_PAGE
configurations.all {
resolutionStrategy {
force 'androidx.webkit:webkit:1.8.0'
}
}
}

dependencies {
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.0"
implementation 'androidx.multidex:multidex:2.0.1'
implementation 'com.google.firebase:firebase-analytics:21.2.2'
implementation 'com.google.android.gmslay-services-basement:18.2.0'
}

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