I'm on the official Android 12 / One UI 4 release and I have noticed the animations while exiting landscape apps is a bit... clunky.
So steps to re-produce:
1) Homescreen should not be set to rotate (i.e. portrait only)
2) Gesture navigation should be enabled
3) Load a landscape app (e.g. a game)
4) Use the swipe to go home gesture
The resulting animations are not as smooth as they were in Android 11 and One UI 3.1. The status bar appears to just jump from the side of the screen to the top. I'm sure it used to fade out then back in. I also sometimes get it where the icon for the app you're in seems to "bounce" from off the screen on to it.
These seem like minor UI issues so hopefully they improve the performance in these scenarios in an upcoming release.