Since updating to Android 13 on a Pixel 4a 5G I am having issues with the miniplayer functionality. It will only appear on the lockscreen or in the drag down menu if I resume playback from within the app itself (widget will resume playback, but will not spawn the miniplayer). The miniplayer will then disappear at some point - I have not identified a cause or timeframe that is consistent, but this behaviour started immediately after completing the update which seems to have also updated the miniplayer appearance.
I haven’t spotted any current topics for this and the troubleshooting that I saw for some of the Android 12 issues hasn’t worked.