Hello. So I started using i3 recently and has been great.
Today I wanted to play a bit of Left 4 Dead and even on Windowed mode whenever I move the mouse pointer the game stutters like if the mouse were leaving the main window of the game. This happens only when moving the mouse pointer and not moving the mouse pointer and clicking for example.
Besides that I read this  reddit post (from 4 years ago) where seems not to be much problems using i3 for gaming at least among the comments of the post. I couldn’t find much more about gaming and i3.