Subreddits were not a problem before since they were accessible on the web without needing an account. But now reddit is gradually locking them down behind authwalls and things like not letting search engines index (other than Google).

Lemmy communities dont have this problem and because lemmy is federated, its resistant to such enshittification (plus you can easily create your own lemmy instance for only your team). So imo they are a good alternative to forums (and reddit) and a good solution to this problem.