In February 2024 Google is shutting down its usenet groups. This is good news because 99.99% of spam is posted through Google.
https://groups.google.com/g/rec.music.folk

You can continue to read usenet through Narkive's web interface - and post too, I think, if you register:
https://rec.music.folk.narkive.com/

There are still active usenet groups, but the folk music ones are unused. The occasional real question does get answered, so there are quite a few people still subscribed.

Newsreaders - e.g. Thunderbird - are mentioned upthread. To post get a free account from Eternal-September
https://www.eternal-september.org/

There's a list of newsgroups in 'Hierarchies' - search for e.g. 'music'.