dns: I would like to create a custom domain on my own name server

You can not completely remove the registry and the domain servers, since no browser can find your domain. So no, what you want is not really possible

A domain must be registered through a registrar accredited by ICANN. That is what the ".com" points to, or its points, then its servers say "check" domain registrar for more information"

Even if you could put this into operation, you might have problems (unless you create your own registrar, which is expensive and not easy)

Anyway, it really would not be beneficial to do it yourself, because Cloudflare had a global CDN that it does not have, and a lot more server power.