alt Hacker NewsIt's a specific setting in XFCE you have to turn on, and most people try to bypass it anyway by manually disabling the compositor with hotkeys. Auto detection of the full screen windows has been hit or miss, especially when running things through proton/wine.
Also with x11 if you go through the steps to get Variable Refresh Rate going and you are dual monitor, it will max the refresh of both to the slowest monitor. :(
Wayland doesn't have that issue.
These are valid concerns for those who spend more time playing maybe. I mostly work, all of my monitors are 60Hz, and I only play single-player games.
If I were into hardcore gaming, and used the same machine for daily work, I would likely just end the X session, and switched to a minimalist Wayland session with a menu of games for the entire desktop.