Oh sorry for the late reply.
Since I stopped using WinFX a couple months ago, I have tried enabling it once in a while across different builds and the problem comes back.
I'm currently in the beta branch. 22H2 Build 23435.1000
I hope is still useful information because of that.
System is a 5900X / 64GB 3600 RAM / 4090
I have 1 x 4K monitor and 3 x 1080p old monitors since years (Muti monitor user since at least 10 years)
EDIT: I just tried again and made a video to show the issue.
Have a nice day.