Developer Joshua Ashton continues doing some great work, as another release of the D3D9 to Vulkan layer D9VK is out.
Released just today, D9VK 0.21 'Lollihop' implements more needed D3D9 features like D3DBLEND_BOTHSRCALPHA and D3DBLEND_BOTHINVSRCALPHA. There's also now support for "locking of MSAA images with intermediate resolve" which is apparently invalid behaviour for D3D9 "but everyone supports this", the YUV2 and YUVY video formats were implemented for compute shaders and some "minor" performance improvements.
On top of that the DXSO shader compiler had more features implemented, more work on Fixed Function support and of course there's a very healthy dose of bug fixing being done to make it more stable. Games like GTA IV, A Hat in Time, The Witcher, Serious Sam 2 and GRID all had issues solved too and bugs affecting multiple titles were also solved.
I'm not a developer, so what does all this gobbledygook mean?
The more of D3D9 that D9VK supports, the more games using DirectX 9 can be expected to work with Wine and so Steam Play too. D9VK was included with Steam Play as of version Proton 4.11-1 released at the end of July, although you still need to enable it manually by adding "PROTON_USE_D9VK=1 %command%" as a Steam launch option for a game.
See the full release notes here.