If you check the graphics options in-game, is the Radeon card listed?

Did you try lowering the game resolution, as well, or switching to Windowed display mode, to see if that would make a difference?

Try verifying local files: in the Steam library, right click on the game and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.

In OSX, disable double buffering, if applicable. If that helps, try triple buffering.

Hold the Cmd button on game startup to get to the configuration menu where you can try enabling the workarounds there.


Try creating a new OSX administrator user account (either with the Documents folder in the default location, or on a different drive, if available), switch to that account and try starting the game from there.

If performance is fine in a new account, but not after switching back to your current account, disable cloud support, if applicable, either globally (in the client click on the Steam menu and select Settings, and then Cloud) or just for this game (in the library right click Divinity: Original Sin 2 and select Properties, then switch to the Updates tab and check the Steam Cloud section).

Next, try browsing to the '~/Documents/Larian Studios' folder and rename the 'Divinity Original Sin 2 Definitive Edition' folder.
This folder contains the saved games, configuration files and a level cache folder. Deleting or renaming it will get the game to recreate it on startup. With cloud support enabled, the client would just download the cloud copy of your existing profile.
After that, start the game and see if the performance is affected. Create a new profile when prompted, and if the initial performance is ok, try starting a new game to test. If that works, exit and copy a couple saves from the renamed folder into the newly created profile's ../Savegames/Story folder. If that continues let you play with normal performance, move the rest of the saves over.
If there is no improvement, delete the new Documents D:OS 2 DE folder and rename the original back again.