I ran into a problem where the EA game wouldn't launch via Steam on my iMac despite there being plenty of resources. It would just "bounce" in the doc and never start.
The fix, for me, was to manually allow the application to have Full Disk Access in the System Preferences:
System Preferences > Security & Privacy > Privacy tab > Full Disk Access (on the left menu) > click the + and add the "Baldur's Gate 3.app" (located in ~/<user>/Library/Application Support/Steam/steamapps/common/Baldur's Gate 3 folder)
(You can also drag the Baldur's Gate 3.app file into the Full Disk Access window)
I am aware that when you first install the game, it prompts you to allow disk access. I installed the game twice during my troubleshooting and I clicked "Allow" both times.
@Larian: I suggest popping some sort of on-screen error if the app doesn't have the file access it needs?
Hope this is useful to other people.