Problem has been solved!
When I did a fresh install of DCS, and went to Mission Editor, it pointed to my "Document\My Games" folder instead of Saved Games - which I know is default. This was certainly peculiar, but since my "DCS Updater GUI Utility" already had a folder under Saved Games and was working fine (able to clear and re-add paths to DCS and Saved Games folder many times over), I did not suspect it much. Out of desperation, I tried to understand why DCS would not pick that folder, so I searched for default location of Windows 11 Saved Games folder and came across this article (https://www.elevenforum.com/t/move-or-restore-default-location-of-saved-games-folder-in-windows-11.8717/). When I typed shell:SavedGames in file Explorer, it did not do anything! Only after downloading the batch file and running it (which opened up my Saved Games folder with "DCS Updater GUI Utility" in it) that I was able to run Model Viewer without crashing! Model Viewer then came up and I was able to load a model without any issue. I then moved DCS's user folder to the same Saved Games and it loaded my config and liveries, etc. This shows that somehow the Saved Games path in the Windows registry must have been corrupted or otherwise become unusable, which resulted to Model Viewer to ill behave and crash. Obviously, in my opinion Model Viewer should handle this more gracefully and in case it does not find a path to the Saved Games folder, it should print a clear message and terminate.
