For the warnings in the question, computeFitSystemWindows and makeOptionalFitsSystemWindows are actually used by the support library or androidx library through reflection. You can verify it by simply searching those two methods in the AppCompatDelegateImpl.
Hopefully this can be fixed later.
Update 1
Recently when I test app in Firebase Test Lab, these 2 APIs and some other APIs are marked
One possible root cause for this warning is Google-owned library UI Toolkit. No action need be taken at this time.
Or
One possible root cause for this warning is Google-owned library Android WebView. No action need be taken at this time.