If you tried the Definitive Edition when you had the previous graphics card, try deleting or renaming the graphicSettings.lsx file in your '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition' folder. That has fixed issues after upgrading a GPU or monitor, though the cases I recall were startup crashes, rather than during gameplay.
Are you shutting down all non-essential programs (especially anti-virus) before starting the game? Firewalls can cause conflicts (generally on startup or loading screens, though) and overlays from graphics tweaking/monitoring programs or chat programs can also caused issues.
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 Files...' 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 you check the Event Viewer, does that give an error code or 'Faulting Module' file name that might help identify the cause of the crash?
- click Start (or WinKey-R), then type "event viewer" into the search box. in Windows 10, 'event' should bring up 'View event logs'.
- after starting the Event Viewer, expand 'Windows Logs' in the left column and select 'Application'
- in the center column, look for a recent error for the game (maybe sort by Date and Time, or search for 'EoCApp')
- check the information under the 'General' tab below the list of events, starting with "Faulting application name..."
Try lowering the graphics settings and resolution, and switch to Windowed or Fake Fullscreen display mode, to see if that will make a difference.
One person reported stability problems in D:OS if they had Ambient Occlusion enabled, for example, but the game was fine if they disabled it and enabled it in their graphics drivers. You could try disabling all the post processing in the graphics options, etc.
Another was getting random reboots, which they tracked down to the graphics options in any game being different than was set as default in their video drivers (for anti-aliasing, ambient occlusion, etc).
Do you have Vsync enabled, or the frame rate cap set in the options? Try enabling, lowering or disabling those options.
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.
If that doesn't help, please email supportdos2@larian.com with a dxdiag report (WinKey-R, type in dxdiag and hit enter, then when it finishes loading click on the 'Save All Information...' button and save the report somewhere handy). Also check the '..\Divinity Original Sin 2\DefEd\bin' folder for the gold.log file, and if there are any 'CrashDump' files being created, zip a few together to include.
Since the crash is fairly consistent at that point, please include your latest save (or a Dropbox or Google drive link, etc). If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.
