It seems like it used to be that only Roblox-created items were sold in the catalog. Then they opened it up for user-created t-shirts. Now it seems like there are a lot of user-created meshes being sold as costumes or accessories.
So how does one go about selling assets officially through the catalog? Or if selling isn’t possible, can I turn a mesh I made into a personal accessory for my own avatar?
You can just create T-shirts, shirts and pants and sell them with premium. For other things like hats and accessories, you would need to be part of the UGC program.
Depends if you’re talking about the Community creations section, those are UGC (user generated content ) that only some specific people can upload to. Roblox gave access to some people who can 3d model to make items.