The vertex shader uses the LIT instruction with negative inputs. DXVK implements this with POW which is undefined on negative inputs and produces NANs for the tex coord.
So how to fix it? I have same issue for Fallout 4 on Windows
The issue in Euro Truck was fixed by us and it'll just work with any somewhat recent DXVK build.
Fallout 4 is a different game that uses a different graphics API. It's completely unrelated. If you want us to take a look, open a new issue and provide the necessary information (logs & apitrace).
proton experimentalx1 2021-09
Software information
Euro Truck Simulator, D3D9 SM 3.0
Screenshots are self explanatory, some weird rendering going on.
DXVK:
WineD3D:
System information
Apitrace file(s)
Log files