It's extremely not legal to sell stuff with other people's art without their permission. This applies to any form, and you can definitely say yes to it being uploaded to one place and no to it being uploaded to another. This is assuming you did not sign a contract that said that they could upload it wherever they want.
Art is something where you do not need to apply for copyright protection, as it all falls under "Intellectual Copyright". This means that as long as you can prove that you made the original art you have an automatic copyright. If you are not being paid for your art and it is being uploaded or sold without your permission I would really recommend contacting whoever is in charge of the project and telling them either to pay you or remove it. If they refuse you can contact Steam/Nutaku/Patreon/Wherever-Else and tell them you wish to DCMA the project. Provide any associated art along with timestamps and they will either take down the project or inform the project managers that they must take it down or risk being banned from their site.
