I only know about because somebody happens to tell me

I agree on that point, I have built a site to check for that https://defed.xyz but you still have to query each instance manually. It's just the way Lemmy works, some research is required when creating your account. I could write you a whole spielt on what criteria you should look at but the short answer is that if you want something big that "just works" lemm.ee might be the place for you.