I revisited Vircadia again for the first time in about 3 years to see how they've been doing. Apparently they're a Browser Experience now... I used to have an AppImage for it, but they no longer appear to provide one... just a Windows binary and browser now, I guess.
There were multiple servers hosting virtual areas, but all with 0 users. Could be a time zone thing, but I'd guess there isn't a lot of user activity in general.
Walked around for a bit, but I didn't get anything out of it I couldn't get more & better from GMod (which I still think would make a better "metaverse" than any existing application).
I read that Decentraland was also a Browser Experience, so I'd like to wander through that next & see how it compares to Vircadia, but I'm not expecting great things.