I disabled DNSSEC from Cloud DNS zone few weeks ago. But still I cannot change the domain name --server with bellow errors.
Updating name servers when DNSSEC is enabled is unsafe. You should disable DNSSEC, wait one day, change name servers, wait one more day then reenable DNSSEC.
I don’t know what is registrar level exactly. But the problem is solved. I retried disabling DNSSEC by gcloud CLI and it works. As soon as I run $> gcloud domains registration configure dns <domain_name> --disable-dnssec it disabled.