I don't believe 396.51 is a hard requirement for DirectX 9 games, only DX12 games and DX11 games via DXVK.
Nevertheless, if you want to see continued support for GPUs which NVidia is dropping support for, you should support the Nouveau project.
Do the Nouveau drivers work with this?
The need for 396.51 will probably be because of DXVK, which needs that driver due to driver bugs.
Nouveau doesn't yet have functional Vulkan support, but it's your best hope of seeing it on legacy cards.
Also, I tested SteamPlay on 390xx, works fine on DDLC, so can confirm 396xx is not a hard requirement.
DDLC is a direct3d 9 game, so there's no surprise in that.
Dxvk doesn't seem to be interested to older gpus (but I may be wrong), so either nag nvidia (for as much as they could add new features to their legacy driver), or make this issue about having graceful fallbacks to opengl.
Closing this issue because it's an issue with the Nvidia driver that will likely be solved with a future Nouveau/Mesa driver, and not an issue on Valve's front.
Friendly reminder mesa is a joke on nvidia cards (or we could say nvidia cards are a joke with it, take your favourite)
Yet the Nvidia driver for my card doesn't support this software and is now legacy. Any suggestions?
Maybe Proton should include the legacy DXVK branch for this, or disable itself in favor of the OGL backend I suppose.
No point in sticking with dead forever software. If any a patch should be sent to workaround the missing extension.
As for switching to OGL, that's an available thing.. I just still couldn't test whether that's automatic though.
The requirement of Nvidia 396.51 means that many GPUs will never function with this software. This should really be changed to at least work with the legacy 390xx drivers.