from the dev:

Performance was 10% worse, and frametimings were less even, but it was certainly playable. This was just how Unity 3D works in Vulkan on Linux, so there was no way to solve it.

Certain parts of this game have geometry that is close together, and on Linux these would flicker. This is because Unity 3D does not support a reversed z-buffer on OpenGL or Vulkan (or DirectX9). This problem is not present in DirectX11+, or Metal. And it’s not present when Proton or WINE convert DX11 commands to Vulkan.

Other than that, everything was the same on Linux as it is on Windows or OSX. We’ve had a native Linux build of this game for its entire life up until recently, just as all of Arcen’s titles have had a native Linux build for the last decade.

So this all feels very strange. But Unity 3D’s support for Linux, and in particular their implementation of Vulkan, is notably inferior to what is going on with their support for DirectX11 and Proton/WINE’s ability to bridge across.