I found a post on Reddit that has a possible solution how to rollback on a mac to Patch 6 before the problems occurred. Scroll down to tenkitron's post.
https://www.reddit.com/r/macgaming/comments/1bag2b5/baldurs_gate_3_fps_drop/I haven't tested it yet, still waiting for the depot download to complete, but may be worth a shot if you don't want to wait for any incoming fix.
EDITED TO ADD:
It works! Any saves made after that patch are no longer compatible, which was expected, but the rollback brought my FPS back up where it was. Worth it if you don't want to wait for Larian to get this fixed for Mac.
Be sure to open BG3 from the file in
~/Library/Application Support/Steam/Steam.AppBundle/Steam/Contents/MacOS/steamapps/content/app_1086940/depot_1419660/
Not through steam launcher.
This worked for me as well! Thank you for sharing.
I moved the .app file from the location you mentioned to:
~/Library/Application Support/Steam/steamapps/common/Baldurs Gate 3/
it saved me around 120GBs to do so.
Also, after you run the app once, you can add it to the Dock while it is running and then easily launch it from there! It works great. So happy to be able to play again.
For anyone struggling with the resolutions acting funny on launch, make sure that you have your Display setting setup so that it matches the resolution setting inside of BG3 (e.g. - Display Setting is 4K for my external display and in game) prior to launch and it will look fine. Otherwise, you can only see a portion of the game. If you need to, search your Mac for "graphicSettings.lsx" and delete it to restore the default settings if you have any issues with graphic errors on relaunching the game.
