Just adding onto the Tumblr answers, since that’s the only place I post art on + where I exclusively look for fanart, too. Like what the first reply mentioned, unless you’re in, like, a really big/popular fandom, you’ll always get notifs on fanart stuff (it’s very funny sometimes because I made fanart on a character’s birthday at least two years ago and I still get notifs when their birthday date comes around LOL). I can’t say much for original art since I rarely do/post it, but I think that as long as you establish upfront that that’s the main thing you post, I don’t think you’ll be ignored (I follow accounts that do original art and occasionally sell their art and although they don’t have as much likes a fanart account would have, I’d say ~20 likes for daily posts + the occasional popular artwork is a good number)?
I used to post my art on Discord quite a bit but I did it mostly because I just loved the media the Discord was on lmao I also used it as a bit of practice for commissions (AKA I just did requests...unpaid :,)), which could be a viable option if you’re looking for something like that since the server I was on was pretty popular so there was always someone wanting something drawn + the artist friends I made on there recommended me other servers specifically for commissions. It’s a good site for making connections, I think :o TERRIBLE for just posting art, though :/