Sadly, there are no "great" options here:-(.

Side-note: "instance blocking" is misnamed, don't be mislead - all that does is mute communities on that instance, but it still shows you all of their comments on posts to communities not on that instance (cough Cowbee cough cough), plus they can reply to you, generate constant notifications (for WEEKS and WEEKS on end if they choose to - it's happened to me, once for hexbear.net and again for lemmygrad.ml, back when my instances were still federated with those, and when I was naive and fresh and had no idea what I was walking into by replying to a post that I had found on All, not having read the community sidebar first), and also they can vote on and influence your content. Only true defederation will prevent the latter though.

1. lemmy.cafe as you saw, but it has some technical problems - e.g. notice how none of the image previews load when you visit? I have no idea what further problems lie behind that one - all I know is that it has persisted for weeks, which does not fill me with confidence. Still, not a bad idea to at least test for yourself?

2. dubvee.org, which has a friendly site admin though a nonstandard (& nonintuitive?) web UI "Tesseract"; he is super aggressive at blocking both the Alt-Right and also the Alt-Left and also trolls regardless of instance; the major down-side being that it is not a wide-spread general-use instance, and limited to W. Virginia USA atm. Anyone who likes to argue may get booted quickly though.

3. quokk.au, although it has only a single admin rather than a team of such, and people say that their requests to join can get ignored for days as a result, also it's in Australia, so with that geographic distance I would worry about federation of content particularly from Lemmy.World that holds ~80% of the Lemmy users and most of the Fediverse content (at least, this is a major issue for Aussie.Zone also in AU). Here too you could make an account and test it out, prior to recommending to friends? If so, let us know your experiences with it?:-)

4. PieFed allows you to block all the users from any instance of your choice without needing a site admin; this Lemmy alternative also has many fantastic upgrades over Lemmy (categories of communities, hashtags, YouTube video embedding, which Tesseract also offers, and more), however it lacks many of the more foundational aspects (user tagging, searching is primitive, many Notifications do not actually go to what they point at so that gets super frustrating), so while I am located there myself this is not something that I would recommend to everyone, only "early-adopters", particularly those who can fall back onto a Lemmy alt when necessary.

5. I have heard that the Sync and Connect apps can block all users from any instance of your choice, without needing admin approval. They have a number of other nifty features as well. I have never used either of these, but these might be your best option?

6. Sublinks... well, that's not an option "soon" at any rate.

7. Otherwise someone would need to spin up a new instance, at which point they can do whatever they choose, but it's a lot of work, particularly a lot of network bandwidth. Or convince an existing admin team to defed from lemmy.ml? It's hard enough for most to decide to defed even from lemmygrad.ml and/or hexbear.net though.:-(

More details

Face it: we are a Nazi bar, or rather the Alt-Left equivalent of one. It takes enormous efforts to carve out a corner of this open social web that fights back hard against a ~~Nazi~~ fascist, and most are unwilling to do what it takes. Though slowly but surely, I do see MAJOR improvements over time - e.g. Discuss.Online recently defederated from hexbear (though unfortunately not also Lemmy.ml), so I view that as a strong even if not entirely sufficient step forward.