If I'm looking for someone who is supposed to have an account on the #fediverse but I never see them, and I suspect it may be because of one instance blocking another instance, what is a good way to find out? Is there something like a public list saying "this instance blocks the following instances because of xyz"?
Best way that I know of is to go to the main instance site. In the about section there is usually a part called "moderated servers". This will show what if any instances that instance blocks. It's rare to see a reason let alone a good one.
For example (near the bottom of the page):
https://mastodon.social/about