Does this happen with the Classic version of the game?
Are you shutting down all non-essential programs before starting the game, especially anti-virus, graphics utilities, or DirectX injectors, etc?
Try resetting your graphics driver's 3D settings to default (right click an open area of the desktop to start the nvidia Control Panel).
Try exiting out of the Galaxy and starting the game directly from the '..\Divinity Original Sin 2\DefEd\bin\EoCApp.exe' program file, by right clicking and running as administrator (or '..\Divinity Original Sin 2\Classic\EoCApp.exe' for the original release).
Try right clicking the EoCApp.exe program file and select Properties, switch to the Compatibility tab, and check off the option to 'Disable display scaling on high DPI settings', maybe 'Run the program as an administrator', and test different compatibility modes.
You can try doing a clean re-install of the graphics drivers. See
here or
here, for example.
If applicable, exit out of Galaxy 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 Definitive Edition' 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 Galaxy running and cloud support enabled, the client would just download the cloud copy of your existing profile.
After that, extract the replacement folder from
this download into your '..\Documents\Larian Studios' folder, and see if that fixes the graphics.
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 helps. If so, you can just create a new profile, if you haven't played enough to bother with any existing saves, or exit and copy the profile folder from the renamed folder into the newly created PlayerProfiles folder.
If you have the same problem, delete the replacement My Documents D:OS 2 DE folder and rename the original back again.
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.
