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