Life has many established processes for getting things done. In a company, for example, if you want to work on a new project then you lobby your boss for resources by providing data about how great your project is.
But I recommend that you just bypass that and you start building in your free time. Once you’ve built something then your boss can see your vision. And the momentum you’ve built will carry the project through to the end.
Yes you run the risk of your boss thinking your project is stupid and wasting your free time. But if you care about the project that much then devoting that time can only make you happier and better at what you do.
Find a way to step out of the process.