According to Steam’s compatibility tool, Borderlands 3 is Playable on the Steam deck with minimal issues.
Borderlands 3 has a Gold rating on ProtonDB, with some users citing issues with black screens and slow load times. While multiplayer seems to be working for some, others mention stuttering and other performance issues.
According to Steam, users on the Steam Deck should not have these issues, stating that the only issues with Borderlands 3 include having to manually invoke the on-screen keyboard and small in-game text that may be difficult to read.
It will be interesting to see if Borderlands 3 will perform as well as Steam is hoping with the latest release of SteamOS 3.0 or if players will continue to have issues.