Just passing on a tip from FediTips I didn’t know about. Using the format
(server)/tags/(hashtag without the #).rss
Your RSS Reader can follow hashtags e.g.
https://mstdn.social/tags/dogs.rss
You can see everything with the hashtag ‘dogs’ on mstd.social and every instance mstdn.social can see.
Is this also possible for Lemmy? Would be nice to get Lemmy community posts3in RSS feeds
Feed for this Community is
https://lemmy.ml/feeds/c/fediverse.xml?sort=Active
you can change the sort to suit you.