On Android 12L, my app won't resize properly (missing resize controls at the top)

I have an app that's designed to run on Android 12 (compileSdk=32, targetSdk=32, minSdk=26). I've set android:resizeableActivity="true" on both the App, and all the Activities in the manifest. And it behaves perfectly fine on older Tablets (tested with API=26), and phones (testes on all APIs between 26 and 32). But when testing it on Android 12L, it launches in "windowed" mode instead of taking up the full screen, and it's missing the resize controls to make it full screen. Here's what my app looks like vs other system apps:

And it also won't behave properly when trying to do split-screen. Again, it works just fine on an Android 12 phone, but on 21L, it just takes up a partial screen instead of filling the right half, as it's supposed to.

It does let me resize it manually (by dragging any of the window edges), but that's obviously not ideal, and makes for a pretty crappy user experience.

I stumbled onto a solution, but it really shouldn't have caused the problem in the first place. It looks to me like there's a problem with the AppCompat library...

My app is build on Jetpack Compose, and all the activities were extending AppCompatActivity (which extends FragmentActivity, which, in turn, extends ComponentActivity). I realized that I didn't need AppCompatActivity, and only really needed ComponentActivity, so I changed all of my existing activities to extend ComponentActivity instead, and as soon as I did that, the original problem was solved.