I've re-added Signal and Discord, and no problems so far...

OK, so I removed two Apple Arcade games, the older non-pro Pixelmator, Discord, and Signal. And now Xcode isn't beach-balling anymore. I *think* I had Signal in place already when Xcode was working before. Discord, now that I think about it, is almost certainly a more recent addition. I totally doubt that Pixelmator is an issue--and I'm almost certain it was already in place--but I did buy Pixelmator Pro, so I don't really need Pixelmator anymore. I didn't delete Pix'Pro, and everything's fine. So I'm thinking about trying to re-add them one at a time to see if Xcode breaks again, but the good news is that after a bunch of random thrashing, something seems to have worked.

OK, one more piece of information: I created a new test account on my MBA and fired up Xcode for the first time and created a new project, just a simple SwiftUI project, a Hello World that would have caused beach-balling in my main account. It worked fine. So there's gotta be some cruft in my setup that's causing this problem. I'll check to see if I have any other programs installed that I might have forgotten about, and I'll uninstall the Apple Arcade games, but... any other ideas?

Just for the fun of it, I removed the watch simulator from the available simulators, then I deleted the com.apple.xcodebuild.plist and the com.apple.dt.Xcode.plist, as well as the com.apple.dt.Xcode directory within my ~Libary/Caches directory. It's still just as bad. Even opening a project it just locks right up.