AbsoVincent

Okay, I think I've overseen this, but I'm already thinking that writing them a second response won't make any difference. I'm sure this entire issue has to do with the game or the wrapper running out of address space due to it being a 32-bit game, and their developer wrote on their GitHub site that it's an issue they're aware of, but unfortunately can't fix.
My goal now is to find a similar wrapper that fixes both the map and random crashing. As forementioned, WineD3D fixes the map crash, but lags terribly making the game unplayable. 
Did you try that already yourself or have a configuration that eliminates the artifacts? In my case, I had the same issue and after quitting the game, it wouldn't start again thinking I'm using an older DirectX version. Otherwise, the game runs fine and the map wouldn't crash anymore, but I'd need to test it out for a longer period to see if the game still crashes randomly or not.
 
 

After thinking a bit about how to resolve this issue completely, I came to this conclusion:
The issue is definitely neither the game itself nor the OS (meaning Windows 10 or 11). It also can't be a CPU, RAM or whatever hardware failure/complication on my side because the game runs without crashes when using Radeon Vega 8 instead of GTX 1650. I can't blame nVidia for this because it's an eleven year old game which has been cut off from most platforms, and if it is a general GDDR6 issue, then it won't be the manufacturer's fault. 
Now, we only have DXVK left. And like I said before: The game runs stable when using integrated graphics, which doesn't need the wrapper for anti-crashing. I wrote an issue to the developers which has been removed and was probably never thought about again. I'll give them a second chance, first using their tool to read out errors when the game is crashing, and send everything to them. More information to follow.

Downgrading can be a possibility but the game runs on Windows 10/11 just fine. I have a PC tower with no graphics card (just integrated Intel HD Graphics) and Windows 10, and although it needs to be set to 720p and mid settings to run the game decently, I haven't encountered a single crash. So it's definitely not the OS's fault.
 
 

Update II:
Apparently, my theory that DXVK might cause the issue has been confirmed. The problem is that the d3d9.dll file is not using enough memory for the game to run, causing it to crash when running out of address space, thus failing to assign more memory. That's probably also the reason why the 4 GB patcher didn't fix the problem, as it only patches the TestDrive2.exe file and not other files. I've put the DXVK log here if someone needs it.
Unfortunately, the developers of DXVK said that it's a known issue and they don't have a solution yet, so until then I'll just play with my integrated graphics when doing longer races, just to be safe.
There's also a megathread regarding this issue on GitHub, and apparently the issue is on both Windows and Linux, and not only TDU2 is affected.
Test Drive Unlimited 2 - Windows 10 Crash · Issue #1819 · doitsujin/dxvk · GitHub
Out of Address Space Megaissue · Issue #1318 · doitsujin/dxvk · GitHub
TestDrive2_d3d9.log