A day we expected to come but now Riot Games have formally announced that their Vanguard kernel-level anti-cheat is coming to League of Legends, and so it will make it unplayable on Linux.
Well, it has been already unplayabe for months. Client works, but when a match starts, you cannot connect to the game. So you get an afk penalty, because their system sucks but the day before it was working fine.
The Steam Deck should be a call to action for devs to support Linux, not the other way around. Good thing I don't play League of Legends or have any interest in Riot games. I can now tune them out the same way I would ignore macOS exclusive software. Neat!