I can't fullscreen video Qubes OS - FIX

Warning: Applying the first solution is potentially dangerous!

There is two ways to fix it.

First Solution:

open your qube settings
click to advanced
on the right you can see allow fullscreen, change use system default to allow
restart your qube (if it is running)

Second Solution (if fullscreen mode FPS so bad):

start your qube
go to video (for this example, i will show youtube.)
you can see on the right-middle on the video, picture in picture button.
when you clicked new tab is opened for video, now do it fullscreen and enjoy your video as fullscreen

Bonus solution: You can research "fps problem fullscreen qubes"