Respawn and EA have today released a major update for the popular battle royale shooter Apex Legends, which gives it an anti-cheat upgrade. Sadly it's causing issues for Steam Deck / Linux players.
It switched from the standalone version of EAC to Epic Online Services anticheat instead, breaking steam deck support in the process.
However, EOS is normally supported on Steam Deck, so this is probably a temporary issue and will hopefully be resolved by either Valve or Respawn/Epic. We'll just have to wait and see.
Edit: this is reportedly now fixed on proton experimental