While you can’t follow hashtags you can follow “topics” like movies, tech, etc. They should do a better job of explaining how to use that feature though.

As for pixelfed, I’d love to use it. But the only use I have for Instagram is following local bands. Although there is a new site that’s popped up recently that’s like Instagram with a forum but only for bands and musicians to communicate with their local scenes. Very cool, old Internet kind of feel to it.