I’ve facing same issue here, after one week of test, the performance issue seems specific to Stray on Proton on Linux on Xen Hypervisor, I’ve tried another game Valheim which known for crappy optimizations and it runs close native performance, but KVM/QEMU can handle both well, I guess I’m out of luck here.
Suffering with Performance Issue with Xen vCPU pinning and GPU passthrough