Are you shutting down all non-essential programs (especially anti-virus) before starting the game?
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. With the GOG version, in the (optional) Galaxy client, select Divinity: Original Sin 2 in the left column, then click on the More button, and in the Manage menu select 'Verify / Repair'.
If applicable, disable Steam cloud support 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). Alternately, exit out of the Steam client, or Galaxy for GOG, and just start the game directly from the executable when required.
Next, try browsing to the '..\Documents\Larian Studios' folder and rename the 'Divinity Original Sin 2' subfolder. 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 Windows user account would effectively do the same thing. With Steam / Galaxy running and cloud support enabled, the client would just download the cloud copy of your existing profile. After that, start D:OS 2, create a new profile when prompted and see if you have the same problem starting a new game.
If that doesn't make a difference, you can delete the new My Documents D:OS 2 folder and (if applicable) rename the original back again.
