Good news: I was able to reproduce the issue following your steps.
Bad news: It also reproduced with WineD3D, ~so I doubt this is a dxvk issue~. Edit: Nevermind, turns out it is a dxvk issue, and a regression in particular.
P.S.: On Wine it's not even "flickering after a few seconds", the white vegetation is very visible and unflickering for most of the benchmark run.
This has been found to be a regression with commit https://github.com/doitsujin/dxvk/commit/7d9864c077e2c583d1656a374b467c10d8e3ff30. That commit was made to fix ATOC issues in Flatout 3 and Injustice: Gods Among Us but seemingly dxvk still is diverting from native behavior as this issue shows.
I have also made a apitrace on amd as it has a different path in the game than Nvidia and Intel https://drive.proton.me/urls/B5G2G7C3G8#uFEGaiXSSkac
Nothing extracted yet.
In Arma 2 Operation Arrowhead, foliage can be observed as white when using ATOC.
Repro steps:
Software information
Arma 2: Operation Arrowhead on Windows 10, for graphics options see the Google Drive download
System information
Apitrace file(s)
https://drive.google.com/file/d/1l2vYG_SiUyck46dnVP4ux5vAnESQQ8WH/view?usp=sharing
^ also includes a readme with repro steps, pictures of graphics settings and the bug and (hopefully) all relevant logs
Log files
Please attach Proton or Wine logs as a text file:
Not using Proton or Wine, dxvk logs found in above download ^
Edit: Removed the word "flickering" to better describe the issue, the foliage is consistently white