We previously covered how enterprising gamers managed to bypass AMD's FSR 4 restrictions to get Redstone frame generation tech working on older RDNA GPUs with OptiScaler. Now, it seems as though OptiScaler has managed bypass another one of AMD's limitations that restricted FSR 4 implementations to DirectX 12 games. According to the build notes uncovered by a Reddit user u/eduhfx , OptiScaler is testing adding Vulkan support in a new test build v0.9.0-pre10. Notably, OptiScaler is using a compatibility tool to work around FSR 4's lack of Vulkan support, similarly to how Linux translates DirectX, calls to Vulkan with DXVK or VKD3D. This also means that FSR 4 on Vulkan should work on Linux systems, as well, where games often run better under Vulkan than DX12—although at the time of writing, FSR 4 w/DX12 currently has issues running on Linux due to a Mesa issue that seemingly cannot be solved by the OptiScaler team.

Added Vulkan w/DX12 support - FSR 4 VK w/DX12, FSR 2.1 VK w/DX12

Currently, known issues :
FSR 4 VK w/DX12 has issues on Linux due to missing Mesa extensions
Not interested in reports as nothing we can fix on our side as far as we know