You can follow Lemmy communities from Mastodon so I would assume it will also be possible from Threads if they federate with at least one Mastodon instance.
It’s not a very Reddit-like experience. I tested it on Mastodon by following a community here and it just spammed my feed with out of context replies so I unfollowed it fairly quickly.
But that experience is likely to improve? And no doubt Meta would like to kill Reddit with the same stone that kills Twitter.