Try disabling shadows in the graphics options. The issue reloading saves may be the same problem as the last post above. In that case, this should be fixed in the next game update (currently being finalised for testing).
In your current user account, if you create a new profile in-game, are the graphics still too dark?
If necessary, hold Cmd on startup to open the configuration menu to disable iCloud saves.
Next, try browsing to the '/Users/<UserName>/Library/Containers/com.larian.dos2/Data/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; playing the game from a different OSX user account would effectively do the same thing. With cloud support enabled, the client would just download the cloud copy of your existing profile.
After that, try starting the game again and see if that fixes the problem with the gamma setting. If so, create a new profile when prompted and exit, then move the saves over from the renamed folder to the new profile's '/Savegames/Story' folder.
If the gamma is still stuck, delete the new D:OS 2 DE folder and extract the replacement folder from
this download into your '/Documents/Larian Studios' folder.
The graphicSettings.lsx file is set to 1280x720 Windowed mode, Very Low quality preset and low audio quality, which you can change in the options (manually, or hit autodetect) if this lets you change the gamma.
If that helps, create a new profile, exit and copy your saves from the renamed folder into the newly created profile's ../Savegames/Story folder.
If that doesn't help, either, delete the replacement Documents D:OS 2 DE folder and rename the original back again.
