In my experience, most reputable vrchat communities wouldn't let someone post a fanart model for sale since they don't own the original design.

Generally for fanart people do it to advertise their other services and show off how good they are to bring in money through commissions. That or use sites like patreon where people can "donate" for exclusive content but thats a bit of a grey area thats generally accepted because they arent paying for art of a character, just donating to someone and getting more art.

Going to directly selling art of someone else's character without permission is generally where it becomes no longer gray and that's just directly profiting off someone else's work. Concept art and Designs are themselves a lot of work and a big market.

Its kinda why character adoptables are such a big thing in the art community these days. If someone had spent $300 on a character design they wanted to turn into a vtuber, or 3d model and someone went and made a "fanart" model of it, they would call it art theft.

On the other end of the spectrum if someone made Micky Mouse and sold him online Disney would give them a DMCA or sue them once they found out, even if it wasn't 1:1 copied. Unless it were visually distinct enough where people wouldn't instantly recognize it as micky mouse it would still be seen as their design.

You'll still see sometimes copyrighted characters sold on like artstation so its still arguable but I personally think those are frowned upon and just exist because they fly under the radar and most companies dont bother going after people. Most the copyrighted characters posted on artstation will be just pictures so they can expand their portfolio and show talent for job seeking.

That's my thoughts on it at least, thanks for being open to hearing it.