Yup. I put in a ticket with Rockstar and here is their official reply. TLDR: Fuck off.

M____. (Rockstar Support)

Sep 17, 2024, 12:51 EDT

Hello,

Thank you for contacting Rockstar Support.

We certainly understand that you are unable to login to GTA online through Steam Deck after the update.

We would like to inform you that the primary goal of incorporating BattlEye into GTA Online is to enhance the overall gaming experience by actively scanning for cheats and exploits, and preventing players with cheats and mods from entering online. The Steam Deck players will not be able to join GTA Online but should be able to launch single-player without any issues. we appreciate your understanding in this matter.

If you have any further questions or concerns, please feel free to let us know. We are here to assist you.

Best regards,

M______. Rockstar Support