When changing the DNS records on the Cloudflare dashboard it is changing the @ value to the domain name which is preventing Ghost Pro to pick it up and activate as a custom domain.
What feature, service or problem is this related to?
That’s just Cloudflare Dashboard display, they both mean the same thing (your root domain name) and function the same. This isn’t what would cause issues with Custom Domains, the most likely case there is they’d want the DNS Record Unproxied , as Proxied blocks them from seeing it, but you’d have to provide more info on what Ghost is saying to know for sure.