I can tell you three you can join successfully, but I won't since as I have said there is currently no way to discover anything about a specific mint. No way to know how long it's been online, how many bitcoin it has, how many guardians it has, who are the guardians and so forth.

BallLightning

looks like we have the same case, I can't join either, it seems limited, I want to try it.

sangekrypto

bitcoin

Mutiny and fedimint

I tried joining a couple but no luck. It seems like many are not accepting new members 