A popular feature of BlueSky that really gets new users’ feeds going is their Starter Packs.
Mastodon Migration Blog is replicating this good idea for the Fediverse with follow packs. These are csv files that can be downloaded and imported into Mastodon to follow a bunch of users around a topic.
PieFed already has categories of communities. It would be hard for Lemmy to copy the code into Rust I imagine. There is an open feature request to add API support to PieFed, at which point perhaps the same front end apps could serve both Lemmy and PieFed? I don’t know which ones may have categories of communities though.