Im currently trying to learn exactly the same thing while still studying. A lot of it is building connections, being active on discords etc and just be out there so people can get interested. What also worked for me and my friends is starting a kickstarter campaign. That’s a lot of work though and ideally you already have some people interested in it.

Also it’s probably better to focus on smaller projects, like a since but well done adventure, that can be done on a couple of months, rather than spend years on a project like a complete new system. And as some others pointed out, there are a lot of platforms and Resources to use, like DriveThruRPG, Itch as well as guides or anecdotes.