Well, here we go again. Apex Legends just launched the Ignite Update, and with it sadly it seems they messed up Easy Anti-Cheat for Steam Deck / Linux.
I've been sent numerous reports on this from players being kicked, and testing it myself on both Steam Deck and desktop Linux - it will kick you out after matchmaking just before you actually get into a game. All you'll see is the below shot and your only choice is to quit the game.
Looking on SteamDB for the update file changes, it seems they removed the needed "easyanticheat_x64.so" file for Linux. This has happened before, and only recently we also had people caught up in a ban-wave that was reversed as well.
So now once again, we play the waiting game until someone at Respawn / EA notice the reports and fix it. Unless it was intentional, we have no idea at this point. The patch notes only mentioned one small anti-cheat update, which was to notify players during a game if a player is removed for cheating.
Currently Apex Legends is Steam Deck Verified.
The trailer for the update is below: