what's the practical way to follow hashtags on instagram?

you can't anymore, as far as i know. instagram took away following hashtags a while back, the follow button on hashtag pages just isn't there now. you can still search the tag and browse it, or save a post from it so you can get back to the tag later. if you want a topic in your feed, follow a few accounts that post about it and interact with them, the explore page picks it up quickly after that.