I looked up preserveLegacyExternalStorage in the AOSP source code, and I found a test which has a comment stating that preserving legacy storage when the app is updated is broken in Android 11 but not in Android 12: https://cs.android.com/android/_/android/platform/cts/+/f0885a38defab0e3cb7e84de225175fabcf52729
So, it's not intentional from Google's side, but the behavior is in AOSP nonetheless. Until you get an Android 12 update, that is.
So, it's not intentional from Google's side, but the behavior is in AOSP nonetheless. Until you get an Android 12 update, that is.