Just before the weekend hit VKD3D-Proton v2.9 was release, giving some big improvements to the Direct3D 12 to Vulkan translation layer used in Proton on Steam Deck and desktop Linux.
Some of the improvements include greatly reduced system memory requirements on the first run of an application, the VK_EXT_graphics_pipeline_libraries extension now used to avoid shader compilation stutter in some extreme edge cases, performance was improved for certain bad occlusion query patterns (Elden Ring being noted here), improved CPU performance of VK_EXT_descriptor_buffer with vendor-specific "ultra-fast paths" and improvements to VRAM oversubscription behaviour if VK_EXT_pageable_device_local_memory is supported.
Various new features were added like better DXR 1.1 support, completed FL 12.1 support, D3D11on12 interoperability interfaces are now supported and added support of VK_EXT_image_sliced_view_of_3d for sliced 3D UAVs.
They've removed the legacy swapchain and they now share code with DXVK which requires v2.1, plus added support for Native Linux swapchain.
Even more game-specific workarounds and bug fixes were made, although they're no longer listing them individually becaise it has become "impractical" to do so. There's also some driver workarounds for NVIDIA and Mesa RADV like a RADV bug causing memory bloat in shader caches.
Work was also done to support the different ways newer games were loading the Direct3D 12 DLL files, as some were assuming a layout like AgilitySDK, so now VKD3D-Proton supports this layout as well (so more games should work).