A few days ago, a page was published in the Fediverse where you could check which Mastodon instance is blocking whom in the Fediverse. This was made possible by a programmer who used the new Mastodon API introduced in 4.0 and automatically read out the blacklists of the instances.
The information about who blocks who is in many ways more than just interesting for those who want to choose an instance. As it was already written in a German thread about the topic, it would be helpful to know whether you reach your target group at all, if you register on an instance.