The SEO crawler that won't stay quiet about your site's problems.
Registrar, when it was registered and when that lapses, nameservers and status -- from the registry over RDAP, the structured replacement for WHOIS.
It asks the registry about a domain and returns what the registry says: the registrar, the registration date, the expiry date, the name servers and the status codes.
It asks over RDAP, the protocol that replaces the old WHOIS. Same information, in a structured format rather than the free text every registry used to write its own way.
clientHold means the domain is pulled from the zone: it resolves for nobody, however healthy the server is.It is one of the most persistent beliefs in the industry and Google has denied it explicitly: domain age is not a ranking factor. What does correlate is that a site with years behind it usually has more content and more links, and those are what count. The date itself does nothing.
My country-code domain returns nothing. That is normal. Many country registries do not publish RDAP at all, or publish it with the data cut back. It is not a failure of the lookup.
Why is the owner missing? Since the GDPR, registries redact the registrant's personal details. What is left is the administrative part, which is the part that is useful here.