Yeah, Mastodon has separate block and mute functions.
Ah, good to know. I'll have to look into it a bit more, but reading https://docs.joinmastodon.org/user/moderating/#block
If you and the blocked user are on the same server, the blocked user will not be able to view your posts on your profile while logged in.
It looks like the limitation that Pamasich and I sort of expected is there. Blocks are basically only possible at your own instance. If the user is on another instance, there's no way to stop them in the fediverse. And that includes it going out to all other instances they federate with too.
I sort of just experienced how this would work if implemented, in a way. A kbin social user posted to a beehaw org magazine. I replied to it, but my post does not seem to have made it to kbin social. However, it's on my instance, beehaw's, lemmy one, etc, because my instance federates with all of those instances. That's sort of what blocking would be like if the original page refused an incoming comment due to a block, all other instances would still accept it. It's possible there's something I'm missing as I'm not super knowledgable on activity pub or the fediverse, so I'll try to learn more about it
I don't know of every instance of course, but from the general purpose ones the order of up-to-date from most to least at the time of posting would be something like: kbin.run, fedia.io, kbin.cafe, artemis.camp (specific API branch), kbin.social.
But there's also other considerations. fedia has a double post/comment issue and a low amount of 500s. Artemis has been giving me a lot of 500s, can't upvote anymore (just reloads the page), commenting doesn't always federate. Many instance admins seem to have disappeared since 3 months ago. I'm not sure what life is like on instances I'm not actively using so there might be issues unknown to me.
Edit: the keys that I look for are localization / ui changes. "more" dropdown now has "more from domain" on updated instances. The UI for the sidebar is different, and most recently the footer is differently styled. There's also the federation list of instances page in the footer now.