The records that matter
A and AAAA point a name at IPv4 and IPv6 addresses; CNAME points it at another name; MX says which servers receive email; TXT holds verification codes and email policies like SPF; NS names the servers authoritative for the domain; CAA limits which authorities may issue certificates.
Changes can take up to the TTL to be seen everywhere, because resolvers cache answers for that many seconds.
Questions
Which resolver is used?
Cloudflare's public DNS over HTTPS resolver, 1.1.1.1.
Why do I see old values?
Resolvers cache records for their TTL. Wait for it to expire after a change.
Can a domain have a CNAME at the root?
Not by the standard; providers offer CNAME flattening or ALIAS records instead.
What is a CAA record?
It lists the certificate authorities allowed to issue certificates for the domain.