I'm not sure about on Linux, but the GPU passthrough on Macos (Fusion) is not like KVM passthrough. When I looked into it I found out it's for one specific use case. Won't increase performance for general apps like Photoshop.
But on Linux, you can do GPU passthrough on Linux for macOS (and Windows) guests.
In particular, since no VM has graphics acceleration for macOS guests, and because macOS relies very heavily on graphics acceleration, GPU passthrough is basically the only way to comfortably use macOS inside of a VM.