If you use an app it may or may not handle it properly or at all, but from the website you should be able to go-to feddit.nl/settings and the block tab and then you’ll have the ability to block users, comms or whole instances from there

I say it’s more of a mute because those users can still interact with your posts/comments (up/down vote, comment on) you just won’t see it. It’s been a highly discussed problem