Can't reproduce, game works fine on my system
Guess the Nvidia driver just crashes for some reason, maybe see if dxvk.halveNvidiaHVVHeap = True in dxvk.conf does anything. Given that no relevant DXVK code is involved when running the game in D3D12 mode, it is extremely unlikely to be a DXVK bug.
@doitsujin investigating it a bit more I found that this problem also appear for some users in Windows. So, it seems to be a Anno bug.
Bug in Ubisoft forum
I can confirm that this bug happens on vanilla Windows. It occured often to some of my friends in Online play - all using Windows. One of them has a 5600XT so doesnt appear to be Nvidia specific.
proton 6.3-7x1 2021-11proton experimentalx1 2021-11
Anno 1800 randomly crashes after some time of game play. The time or action this occurs seems to be random. When it freezes and crash, a small window pops up like the screenshot bellow.
This problem happens with DX11 and DX12.
It also show some messages in the terminal:
Software information
Anno 1800 from Ubisoft Connect using Proton Experimental
System information
Log files