Most significant with VKD3D-Proton is early, work-in-progress support for Direct3D 12's DirectX Ray-Tracing (DXR) implemented atop Vulkan ray-tracing. For those with a GPU/driver supporting Vulkan ray-tracing, VKD3D-Proton is beginning to work with "real content" albeit still work-in-progress and a limited number of games working. The Radeon Software Linux driver released this week with Vulkan ray-tracing also isn't working so for the moment is just the NVIDIA proprietary driver.
Games tested with VKD3D-Proton's DirectX Ray-Tracing are Control and Ghostrunner.
VKD3D-Proton 2.3 also brings conservative rasterization tier-3 support, variable rate shading tier-2 support, and various game fixes. There is also better performance in GPU-bound situations by up to 20% on NVIDIA for RE2, support for async compute queues, and various other performance optimizations and fixes.
More details on VKD3D-Proton 2.3 via GitHub .