PSA: You should know that Settings > Migrate Subreddits exists. All you do is login to your old Reddit account, copy a “multireddit” link, paste it in Voyager and you’ll be able to search the fediverse for those topics/communities to subscribe to.

You may find communities that are missing here if you’d like to run/manage your very own community on a topic you enjoy.

Hope this helps. I just found this feature today and subscribed to a bunch of communities.