@cchcyx463 I did some tests but I couldn't find a way to change the popup positions besides dragging it with the mouse. The position is stored somewhere but I couldn't find it.
I tried disabling and re-enabling it but the position wasn't reset.
opera://settings/videoPopout
Changing the browser window size didn't help. Did you at some point change the screen resolution or the font size in Windows to something like 125% or 150%? Or maybe did you use dual monitors?
If you open a private window, the popup should appear at the bottom right corner. If that works, it's just a matter of finding the window in some screen border or deleting the saved coordinates.