

PieFed is a 100% for this.
Topic-focused puts you into the Threadiverse, where there are mainly 3 options: Lemmy, Mbin, and PieFed. I haven’t looked at nodeBB but that’s a fourth up-and-comer. (Also people expect flarum to gain ActivityPub support but it currently lacks it.)
Mbin’s major claim to fame is combining the topic-focused Threadiverse with the user-centric Mastodon like sharing, which sounds like not what you want… although it does have hashtags, and yet iirc only on the Microblogging side?
A very few - and unfortunately no longer maintained - Lemmy apps have some of what you want, but it is not worth what you would lose out on by doing so.
PieFed has perfectly what you have asked for. Hashtags sit on top of regular communities, so it is not either-or but rather both capabilities at the same time. And while I don’t know if you can block a particular hashtag (that feature should be added, if not, it’s a great idea!), the concept of keyword filtering (regardless of hashtags) can not only block out all of such content, but there’s even an option to only block out some, if you would rather, so that additional level of choice is nice. The only catch is that app support is experimental at best, so make sure to use the web browser view, at the very least to set up your account with the blocking that you want to see associated with your account, even if you then use an app for just daily browsing.
As Rimu (inventor of PieFed) already said, PieFed has numerous other features that you will fall in love with as well - e.g. categories of communities, which are both customizable and user shareable (so you can create a curated one if you like, and then share with literally everyone housed on the same instance, but there are pre-defined ones so that you do not have to) and many other features lacking on Lemmy such as user and post flairs, ability to hold polls, and just an absolute ton more behind all of that. It even goes further in terms of features than Reddit does, e.g. combining all the comments across all reposts of a particular OP into one view, to help deal with the fragmentation inherent in an implementation of the ActivityPub protocol i.e. the nature of the Fediverse trends towards fragmentation so this helps counter-balance that.
Happy explorations!
We are using their tools though…
Well, you are, while I am on PieFed:-P If you do not like what you’ve heard here, then consider switching to Piefed.World (Lemmy.World’s recently-announced PieFed replacement for Lemmy)