Hey, thank you for bringing this up, we'll try to identify the issue on linux environment, and regarding the shadow, it is disabled when you're in lowest settings, but should run just fine the rest, but we'll take a look on that for sure
So I have some good news and bad news. Good news is I have since upgraded my CPU from the i7-6700 to an i5-12600K and now the frame rate issues are fixed. Even on ultra settings at 2560*1440 it didn't drop below 60 FPS. The bad news is that now if I set the graphics above "Low" the screen flickers constantly.
Intel i5-12600K | 16GB DDR4-3000 CL15 | XFX RX 590 8GB Fat Boy | Mesa 23.1.7 | WD SN850 500GB | Solus | Mate 1.27.0 | Kernel 6.4.15-254 | MSI G2730QPF 2560*1440 @ 165hz