

On every website I’ve ever ever been on, opting in for NSFW means opting in for porn. If you don’t want porn, disable NSFW, and block any communities that don’t use proper NSFW tags. If you want to sometimes view NSFW/porn, but not always, make an alt account, preferably on a NSFW-focused instance.
I learned this lesson on Mastodon, but all means ALL. It is an uncontrolled firehouse of posts without any algorithm to filter it. By design, if a single BeeHaw user subscribes to a porn community, then the entire instance shows up in everyone’s all feed, unless BeeHaw defederates.
You could always make a feature request with the Lemmy devs, but they are swamped with all the bug reports and feature requests. There is no way to tell when or if the feature you’re asking will be implemented, and when BeeHaw will update to it. So to answer your question, no there isn’t. You’ll need to disable NSFW.
I mean, anything is possible with enough programming skills and an API. And I did find multireddits to be very useful on Reddit. But I don’t think creating a “one true meta-community that replaces r/whatever” is either feasible or desirable.
Firstly, what your talking about want even possible on Reddit. Subreddits are infamous for fracturing over mod drama. Look at the Game of Thrones/ASOIAF subreddits. There’s the main sub r/ASOIAF which is for any media from the ASOIAF series which split into r/PureASOIAF for JUST talk about the books. R/GameofThrones was for talking about the TV show, but users hated how strict rules were for spoilers, so users went and made r/freefolk which got more popular than the original sub.
Second, at a fundamental level, Lemmy and any Fediverse social media is about decentralization. Even if you were able to develop such a tool over the top of Lemmy/Kbin, a meta-community wouldn’t really be centralized, as each community would have its own moderation team with its own rules. If one community defederates from any of the others, it would break the meta-community. Additionally, instance admins and community moderators might also oppose the tool if it brings an influx of outside users who aren’t subscribed to posting and commenting in their communities.
On both Reddit and Lemmy, anyone at any time can make their own subreddit/instance and host any new communities they want. People are going to organically pick whichever community fits the thing they’re looking for. That’s not always the same thing, and that’s a good thing. Some people want strict moderation and enforcement of being on-topic, some people don’t. Wishing your favorite subreddit hadn’t shut down or splintered doesn’t undo that it happened. Wanting an “official” community for your old favorite subreddit is unlikely, but possible. Wanting your community to be the “official” community across all of Lemmy & Kbin is unreasonable.
My suggestion is to hang out and see how the Fediverse works. Subscribe to some places and migrate your account if you don’t like the vibe of an instance. But Lemmy (and BeeHaw especially) aren’t trying to recreate Reddit exactly. This is our version of a link aggregate social media site, and sometimes not being like Reddit is intentional.