I was looking for a place to share my two favorite Mastodon and Lemmy clients, they are called Voyager Connect Boost for Lemmy and Moshidon for Mastodon (if you are really serious about privacy I recommend Connect still)
(the official Mastodon app works fine though, you just can’t follow new hashtags from it)
They are very good, try them out sometime 👍 (I’ll update this post whenever my opinion changes)
The official Mastodon app doesn’t support following hashtags, for some reason (the Mastodon website does, but the app doesn’t)
I haven’t had an issue with following hashtags with the official app. I can even get a list of hashtags I’m following.