If you want to support individual creators, Etsy is a great place to start. Millions of people put their original work and handmade items on Etsy every day.
I like Artpal because you have the option to not only sell original paintings but to sell prints as well. It’s a cross between an online gallery and a print-on-demand platform.
Fine Art America is very similar to Artpal. Independent artists can upload their work to the platform without having to be curated.
Artspace is an online gallery that curates the work of professional artists from around the world. They partner with galleries, publishers, and even museum.