It depends how you're accessing Lemmy.
On the website, you can click on the 3 vertical dots near the post or comment, and chose 'Block User' from there.
On the Voyager app, you can click the user's name, and then select it from the 3 horizontal dots.
It might be that whatever app you're using doesn't support it. Before Voyager did, I used to go into my Settings and then search for the user (e.g. [at] bot [at] lemmit [dot] online) in the 'Blocks' sections.
Yeah, at least c/antiquememesroadshow uses a new concept with reliving meme nostalgia, and refugees of r/prequelmemes, r/sequelmemes and whatever the OT meme sub is have united into one community here- as have the state-themed subreddits for Washington, Oregon and Idaho with c/pnw.