Cloudflare supports domains that only use an IPv6 server IP address. You would need to add the records in your DNS settings as an AAAA record type. To add an AAAA record:
- Login to your Cloudflare account.
- From the dropdown menu on the top left, select your domain.
- Select the DNS settings tab.
- Add your AAAA record values, for example adding an AAAA record for the root.