Multi-reddits are a frequently requested feature and there's a GitHub issue for them: https://github.com/LemmyNet/lemmy/issues/818
Core devs for the most part are focused on existential issues like performance (slow DB queries are responsible for the denial of service attacks that are taking lemmy world down daily) and moderation tools (lack of which are responsible for major instances defederating with each other rather than moderating more aggressively). Unless a community dev steps up to work on multi-reddits, it's likely to sit at the back of the line for a few months.
It's also possible that some app will jump the like with client-side-only multireddits. If that's a thing, I haven't heard about it yet. Maybe someone else will chime in if they have.