New domain registration is still a Beta product and we will make sure to announce it in all channels once it is GA.
For now, please activate your domain on Cloudflare and you will be able to transfer it to Cloudflare Registrar.
Make sure you understand current limitations:
The main 2 limitations are:
- you have to use the assigned Cloudflare nameservers
- you cannot move the domains to other Cloudflare account