The one caveat is that from Lemmy instances, the community doesn’t have show old posts (see https://lemm.ee/c/barcelona@piefed.social), but if you were restarting a community from scratch you wouldn’t have access to your old posts anyway.
This ensure that at least the posts are transferred to a community on an active instance, which is probably the main concern for lemm.ee communities at the moment.
Have you an idea on what instance you want to migrate already?
I have had a real fine experience with sh.itjust.works (and with the French Jlai.lu, but this one is focusing on French language ;)
We might use the Piefed community migration feature: https://piefed.social/post/667045
I just tried it on !barcelona@lemm.ee to !barcelona@piefed.social, it worked quite well
Do you see the old posts from lemmy?
https://lemmy.dbzer0.com/post/45876492?scrollToComments=true
Ah, guess that makes sense. Thanks.