I'm gonna miss r/Art that's for sure! I loved how ppl gave different techniques a twist. It gave me hope! Most websites circlejerk around portraits and anime.
Also r/depression. I use to reply post when I think I could say something helpful. Today someone committed to hospital and I'm afraid she won't be able to reach us back, ask for help, ask for someone to listen her.
There's lots of niche hobbies too. I recently joined 3 and I was thrilled with these communities: r/falloutnewvegas and their witty crossovers, r/Tau40K had some cool painters and, oh boy, r/MechanicalKeyboards.