I used to have the same thing, and it's a pain trying to get complete none-flickering (impossible maybe)...
I played around w the settings and I'm not disturbed anymore by the shadows. I will list here the settings I settled with and are related to shadows.
Give them a try , but all systems are different ... could be what works for me does not mean it's good for you
(I run an NVIDIA 4080s on a Quest 3 w Link cable, you might have a whole different setup...).
settings AC VIDEO:
(I also have shadow res on 6144x6144 in )
View attachment 1453089
Settings CSP - General Patch Settings:
View attachment 1453086
Settings CSP - GRAPHICS ADJUSTMENTS,
View attachment 1453085
Settings CSP - Smart Shadows:
View attachment 1453088
In NVIDIA settings:
View attachment 1453090
(some say it's better to turn Anisotropic filtering on in here , and OFF in Assetto ...
View attachment 1453091
play around w these and see what is best for you)
hope this helps ...
Good luck!