Some intrusive ones (EA's anti cheat for recent Battlefields, Activision's anti cheat for Call of Duty, anything from Riot to name a few) do not work.

However, EAC - who is a major player in this field producing generic solutions - does support Linux. The involved publisher, however, needs to approve this and the developer need to turn on a feature flag. That's it.

However, some publishers simply deny this for... totally mental reasons ...and this means that the game is marked as borked in protondb even though the game could as easily be played on Linux thanks to EAC's Linux support.

"EAC supports Linux, but devs just won't turn it on" is the clickbait answer, but the details are more nuanced. EAC has multiple security levels that a title can set based on the threat model of the game, and most games with heavy MTX that use EAC shy away from it, largely because Fortnite doesn't do it. EAC is owned by Epic, and if Tim Sweeney says that you can't do MTX on Linux safely, then any AAA live services game with in-game MTX is going to shy away from it, regardless of how true the statement actually is.