What you're asking for never existed. Reddit had multiple subreddits devoted to those subjects. Forcing there to be only "one true" community for any given subject is antithetical to the whole concept of free association and free speech, there's always going to be people who disagree with how the subject matter has been divided up and how it's being moderated. They'll want to create their own groups.
You're probably wanting something like Reddit's "multireddit" functionality. I know of this issue for Lemmy, with some links to related issues in the comments. Kbin has one here.