I just upgraded Android Studio to the latest stable version (Arctic Fox 2020.3.1) on Mac, and now my project doesn't build. I get a "Kotlin not configured" in the IDE top bar, and in the build output I get this error:
Could not find org.jetbrains.kotlin:kotlin-android-extensions-runtime:1.5.21.
Required by:
    project :app
I tried to add this dependency to the app module Gradle file, but the error remains:
implementation "org.jetbrains.kotlin:kotlin-android-extensions-runtime:$kotlin_version"
For your reference, here is my Project Gradle file:
// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    ext {
        kotlin_version = "1.5.21"
        version_navigation = "2.3.5"
        version_lifecycle_extensions = "2.2.0"
        version_lifecycle = "2.3.1"
        version_room = "2.4.0-alpha04"
        //version_room = "2.2.6"
        version_coroutine = "1.5.0"
        version_retrofit = "2.9.0"
        version_moshi = "1.9.3"
        version_retrofit_coroutines_adapter = "0.9.2"
        version_glide = "4.12.0"
    }
    repositories {
        google()
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:7.0.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version"
        classpath 'com.android.support:multidex:1.0.3'
        classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$version_navigation"
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}
allprojects {
    repositories {
        google()
        jcenter()
    }
}
task clean(type: Delete) {
    delete rootProject.buildDir
}
And here is my Module Gradle file:
plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-android-extensions'
    id "org.jetbrains.kotlin.kapt"
    id 'androidx.navigation.safeargs'
}
android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"
    defaultConfig {
        applicationId "com.virtualsheetmusic.vsheetmusic"
        minSdkVersion 21
        targetSdkVersion 30
        versionCode 20
        versionName "2.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        multiDexEnabled true
        vectorDrawables.useSupportLibrary = true
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
    buildFeatures {
        //dataBinding includes viewBidning below https://stackoverflow.com/questions/58040778/android-difference-between-databinding-and-viewbinding
        dataBinding true
        // for view binding only:
        // viewBinding true
    }
}
dependencies {
    //implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
    //implementation "org.jetbrains.kotlin:kotlin-android-extensions-runtime:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.6.0'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation "androidx.fragment:fragment-ktx:1.3.6"
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0'
    implementation 'androidx.navigation:navigation-fragment-ktx:2.3.5'
    implementation 'androidx.navigation:navigation-ui-ktx:2.3.5'
    implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.3.1'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    implementation 'com.jakewharton.timber:timber:4.7.1'
    //Lifecycle and LiveData
    implementation "androidx.lifecycle:lifecycle-extensions:$version_lifecycle_extensions"
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$version_lifecycle"
    //Room
    implementation "androidx.room:room-runtime:$version_room"
    kapt "androidx.room:room-compiler:$version_room"
    // Kotlin Extensions and Coroutines support for Room
    implementation "androidx.room:room-ktx:$version_room"
    // Coroutines
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$version_coroutine"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$version_coroutine"
    // Testing
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    //For Internet connectiona and JSON stuff...
    // Moshi
    implementation "com.squareup.moshi:moshi:$version_moshi"
    implementation "com.squareup.moshi:moshi-kotlin:$version_moshi"
    // Retrofit
    implementation "com.squareup.retrofit2:retrofit:$version_retrofit"
    //implementation "com.squareup.retrofit2:converter-scalars:$version_retrofit"
    // Retrofit with Moshi Converter
    implementation "com.squareup.retrofit2:converter-moshi:$version_retrofit"
    implementation "com.jakewharton.retrofit:retrofit2-kotlin-coroutines-adapter:$version_retrofit_coroutines_adapter"
    //Glide
    implementation "com.github.bumptech.glide:glide:$version_glide"
    annotationProcessor "com.github.bumptech.glide:compiler:$version_glide"
    //Recyclerview swipe-refresh...
    implementation 'androidx.swiperefreshlayout:swiperefreshlayout:1.1.0'
    //For PDF and download management from here: https://blog.mindorks.com/how-to-open-a-pdf-file-in-android-programmatically
    //https://github.com/barteksc/AndroidPdfViewer
    //implementation 'com.github.barteksc:android-pdf-viewer:2.8.2'
    implementation 'com.github.barteksc:android-pdf-viewer:3.2.0-beta.1'
    //implementation 'com.mindorks.android:prdownloader:0.6.0'
    //This below to handle double clicks...
    //implementation 'com.gitlab.developerdeveloperdeveloper:androidutilslibrary:1.0.0'
}
I have already tried this:
- Build: Clean > Build
 - Invalidate Caches / Restart
 
Any help is appreciated thanks!
UPDATE:
I solved this problem by adding back the jcenter() repository in the Project Gradle file which I removed because Android Studio marked is as "deprecated" (barred).
Now I get this other error, and I have no idea how to solve it:
Execution failed for task ':app:kaptDebugKotlin'.
> A failure occurred while executing org.jetbrains.kotlin.gradle.internal.KaptWithoutKotlincTask$KaptExecutionWorkAction
   > java.lang.reflect.InvocationTargetException (no error message)
Any thoughts? Thanks again.