Thanks for the tip. I tried out 6.1.6-arch1-1 and still had no luck. Digging into that Steam error I mentioned in the first post, it sounds like Error: OpenGL GLX extension not supported by display may be due to mesa being built against an older llvm version. It looks like I've got 2 llvm-libs-git versions, and the older one is probably the one that I want, since it's from mesa-git. I'd upload a screenshot, but apparently I can't because I'm a new user.
Anyway, the problem now is that I've got these two different versions of llvm-libs-git installed. One's from chaotic-aur and one's from mesa-git. The chaotic one is the most recent, so it's active. I'd like to get rid of it, but if I try to uninstall it, it's going to take a thousand or so packages with it because they're dependent. What I really want to do is just swap those dependencies over to the other version that I already have installed. Is that a thing I can do?