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 lowering the desktop resolution, and refresh rate (if it is higher than 60). A program like
DesktopOK would let you save and restore desktop icon positions, in case lowering the resolution moves anything.
Try setting the game to run on the integrated graphics. They are not officially supported, but as long as they have hardware support for DirectX 11 (HD 4000 or later), they should be able to start the game (performance wouldn't be as good, of course, but you only need to be able to check if you can get into the graphics options, and change them there, if possible).
The location varies a bit depending on the GPU and driver version, but in the options there will be a section where you can set specific applications to run on either the 'high performance' GPU or 'power saving'.
You may want to try a clean re-install of the nvidia graphics drivers. see
here or
here, for example.
It is possible to manually change the resolution and display mode by editing the graphicSettings.lsx file (in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition' folder), in Wordpad or other text editor. If you have any issues with that, deleting the file will get the game to recreate it the next time it is started, or you can re-extracting it from the replacement D:OS 2 DE folder download.
To change the resolution, search for 'ScreenHeight', and edit the resolution in the value="xxxx" terms (shown below for 2560x1600 resolution):
<node id="ConfigEntry">
<attribute id="MapKey" value="
ScreenHeight" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value"
value="1600" type="4" />
</node>
<node id="ConfigEntry">
<attribute id="MapKey" value="
ScreenWidth" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value"
value="2560" type="4" />
</node>
Search for 'fake' near the start of the file to set the display mode. Edit the number in value="0" or value="1" in the second line after FakeFullscreenEnabled and / or Fullscreen; if both FakeFullscreen and Fullscreen are set to zero, it will be in Window mode).
<node id="ConfigEntry">
<attribute id="MapKey" value="
FakeFullscreenEnabled" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value"
value="0" type="4" />
</node>
(and a couple entries lower)
<node id="ConfigEntry">
<attribute id="MapKey" value="
Fullscreen" type="22" />
<attribute id="Type" value="0" type="5" />
<attribute id="Value"
value="1" type="4" />
</node>
