Except a lot of anti cheat now supports Linux. Destiny 2 doesn't run on Linux only because Bungie refuses to allow it, their AC supports Linux just fine now
But the steam deck really disproves the notion that Linux can't run these games. The companies that make them choose not to support Linux, and in that way its not really Linux's fault that the games don't work.
Exactly this, the community has proven it will put the effort to make it work, and a lot of things that don't still are because the companies resist it intentionally