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

mapping.txt location
/app/build/outputs/mapping/release/mapping.txt

Seems like 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][1]. 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.(According to [this][1])
[1]: https://github.com/apache/cordova-android/issues/1008#issuecomment-682092997