Server Version: V1.40.1.8227
Player Version: 10.11.0.183
I once switched to PiP on my Pixel 7 and was a short period in landscape.
Then I watched the movie further.
Since then I always have a PiP shadow on my screen when the phone is in landscape and the shadow is unmovable or removable.
Even force closing Plex or System-UI fixed it.
I guess a phone restart might fix it, but I don’t want to do that every time I watch a movie…