Are you shutting down all non-essential programs (especially anti-virus) before starting the game? Firewalls have caused conflicts (generally on loading screens) and overlays from graphics tweaking/monitoring programs or chat programs have also caused issues.
Try starting the game without Steam running: right click the game in the Steam library, select Properties, switch to the Local Files tab, click on the 'Browse Local Files...' button and then exit the client and launch the game from Finder.
If that doesn't help, try browsing to the '~/Documents/Larian Studios' folder and deleting the 'Divinity Original Sin Enhanced Edition' subfolder.
This folder contains the saved games, configuration files and a level cache folder. Normally I would suggest renaming the folder for troubleshooting purposes, but if you don't have any saved games that isn't an issue.
Next, extract the replacement folder from the download below into your '~/Documents/Larian Studios' folder, and see if that will let you start the game (it may help if the problem is in setting up the initial Documents folder and configuration files).
https://www.dropbox.com/s/1ipz4q9780x35tj/DOSEE_doc_20119430.zip?dl=0The graphicSettings.lsx file is set to 1280x720 Windowed mode, Very Low quality preset, which you can change in the options (manually, or hit autodetect) if this gets the game to start.
If the game still crashes, you can delete the downloaded Documents D:OS folder.
What are your system specs, particularly the graphics card?