@winter@social.translunar.academy For Japan, there is a MastoArt alternative, Misskey.io, which is also large (larger than MastoArt, in fact) and open to artists. In fact, it has possibly one of the largest art communities in the Fedi. I hope someone takes cues from that instance to serve artists outside Japan.
I'm not sure what to say about Global Fedi users, though. I guess they can just stick to a generalized instance. It's not perfect, as you don't have a dedicated art community, but at least they can slowly create one off of following artists that show up on the Federated timeline. I follow numerous artists and post art on my berserker.town account, for example. I have to rely on this account to find Misskey artists (since it moreso fetches Japanese text messages which I cannot read), but it's nice exploring the home timeline and seeing the cool stuff people have posted (moreso cause' they'll boost and thus promote new artists to follow).