The DXVK 1.9.1 release comes one and a half months after DXVK 1.9 to improve support for various games, including Roblox, which should perform much better on NVIDIA GPUs, Risen 3, which should no longer crash on NVIDIA GPUs, as well as GTA IV, which should no longer break when playing with an NVIDIA graphics card.
The Roblox performance improvements were achieved by rewriting the way staging textures are handled in D3D11, which also reduces memory usage and the number of image copies needed to move data between the GPU and CPU.