There are several places you can discuss abc notation, swap tunes, ask technical questions and find other abc users.
abcusers mailing list
... the abcusers mailing list is long established group for discussing abc notation and the software tools to handle it (originally on yahoo, migrated to groups.io December 2020). Since several of the abc software developers subscribe, it is a great place to ask technical questions or start a discussion about issues arising from using the notation.
abc notation users group on facebook
... the facebook ABC Notation Users Group is "a place for day to day users of ABC Notation to discuss ABC, seek answers to questions and share knowledge about the way ABC works and what it can do".
As well as usenet groups such rec.music.celtic and rec.music.folk, other places that are good for abc hints and tips, or swapping tunes, are community sites such as thesession.org (mainly Irish & Scottish music) or Mudcat (mainly folk song) where a lot of abc users hang out.
For more specific enquiries, see the contact page.