Try browsing to the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition' folder and delete or rename the graphicSettings.lsx file, to get the game to recreate it the next time it is started.
If that doesn't help, try downloading this replacement folder
and extract just the graphicSettings.lsx file from the zip into your D:OS 2 DE folder, to see if that will get the game to start properly.
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 that helps.
Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer.
Run msconfig again to switch back to the normal boot configuration.
Try creating a new Windows administrator user account, switch to that account and try starting the game from there, directly from the executable.