In your main user account, if you browse to the '/Users/<UserName>/Library/Containers/com.larian.dos2/Data/Documents/Larian Studios' folder and rename the 'Divinity Original Sin 2 Definitive Edition' folder, does that let you start the (game multiple times) with cloud saves disabled?
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 (or if cloud support was enabled, the client would just download the cloud copy of your existing profile).
If the game still crashes the second time you try starting it (ie if there are existing configuration files, etc, in the data folder for the game), try deleting the new folder and extract the replacement folder from this download
into your 'Larian Studios' folder, and see if that will let you start the game.
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 gets the game to start.
If that helps, create a new profile, exit and copy a couple saves from the renamed folder into the newly created profile's ../Savegames/Story folder. If that continues to let you start the game (and load the saves), move the rest of the saves over.
If the game still crashes, delete the replacement Documents D:OS 2 DE folder and rename the original back again.
Try doing a clean boot and then test the game; if that helps, there may be a background program or service running in your current account that isn't in the new one. Start/restart your Mac and hold the Shift key down as soon as the progress bar comes up in the startup window, releasing it after the desktop appears. Alternately, from the login window, hold the Shift key when you click the Log In button, and release it when you see the Dock.
If neither help, please post/PM your system specs, or email email@example.com; you can use the 'System Report' button from the 'About This Mac' Apple menu item, or the 'System Information' app in the utilities folder), including the OS version number, Mac model name and year (indicating early/mid/late) and model identifier.