One of Steam's Most-Played Games Is Now "Unsupported" on Steam Deck
"Steam Deck does not support BattlEye for GTA Online. You will be able to play GTA5 Story Mode but unable to play GTA Online ," said Rockstar's note on the matter. " GTA5 and GTA Online are not officially supported on Steam Deck and all technical support questions should be directed to Valve's Steam Deck support content and community."