I had to remove Steam before lib32-nvida-utils would go - now Steam won’t reinstall
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Got it with --assume-installed lib32-vulkan-driver
Let’s see if it works :)
[edit]
Nope. Builds shaders (a little too quickly perhaps) and then stops.
Skyrim still works, which suggests that the problem is with version of proton and environment variables rather than the beta drivers. And at least I’m no worse off than before.
I might give this another go tomorrow - look at it with fresh eyes and all that.