Steam supports a lot more titles on Linux, but some will never work right (Cuphead takes some effort to get working etc.)

Best to check your favorites are functional before nuking Windows, or do the dual ssd OS boot option. =)

Cuphead works fine on Steam Deck. Valve did that effort.

Steam did a lot for playable titles with Proton.

It is a lot less of a pain for Linux users these days, but still YMMV =3

This is true, there are a select few that use a particular anti-cheat that doesn't work on Linux and that's unfortunately unavoidable. That said, as others have stated, several of them do work like Easy Anti-Cheat, which means I can happily play those online without getting kicked.

I play Battlefield 2042, Call of Duty Warzone, Apex Legends, PUBG, Rainbow 6 Siege, and Fortnite all somewhat regularly and none of these as far as I know work.

The only games that I do play regularly that work are Counter Strike 2 and DotA. Though I can't use Faceit for CS2 which would be ideal.