In particular, on my server the RSS feed for #Bikenite is
https://mastodon.sdf.org/tags/bikenite.rss
You may want to put your own server domain name in place of 'mastodon.sdf.org' Because of the peculiarities of federated messaging, there's no guarantee that all #BikeNite messages are on every server. Instances with more people tend to receive more messages than smaller instances. That's why group messaging like @bikenite exist.
#BikeNite A3