Android version release warning message: This App Bundle contains Java/Kotlin code, which might be obfuscated

Mostly it's a warning message coming from the new play console, you can solve it just by setting your minimum api level to 29 or even better by uploading the retrace mapping file as described here. Enable minify 

buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'),'proguard-rules.pro'

        }
    } 

After building apk/app bundle you can find /app/build/outputs/mapping/release/mapping.txt file . New console will allow you to upload mapping.txt along with your apk or bundle. You can find this option from App bundles and APKs menus.