I too have this issue on desktop and sd, always into the 40s when reflections are around and reported it to the linux gaming dev discord steam deck channel before, can confirm it is definitely not a dxvk issue.
Seconding this as I was about to open a thread as well. I made a thread with DXVK as I thought it could've been due to that but it seems like a Proton issue this time as Windows-based systems do not have this issue. It d...