That’s a common glitch on Lemmy right now. Subscribing to communities oftentimes gives you that message, but as far as I’m aware they’ll still show up in your feed like normal. I’ve heard if you click subscribe and then let it sit for a while it can resolve itself to show you as fully subscribed, but I haven’t had much luck with that.
Smartphones (and the Internet more generally) have led to a major decline in reading books among the American public. I think this plays such a huge role in the absolutely batshit crazy cultural shift we’ve seen.