The new kid on the block here is FragPunk, an online competitive FPS that feels like a noisy flashy version of Counter-Strike blended with Valorant and the good news is the anti-cheat is enabled for Linux / Steam Deck.
An issue I have observed on my desktop though is that the mouse likes to leave the screen. I had to set it to Fullscreen, instead of a Borderless Window to get around the issue.
People are still playing on borderless windowed?
Borderless windowed is not the same on Linux as it is on Windows. It doesn’t make a difference.