Apex domains cannot have CNAME records.
Question and response
Question
dig 10.authorize.certificatemanager.goog. NS
Answer
10.authorize.certificatemanager.goog. 5 NS ns-cloud-c3.googledomains.com.
10.authorize.certificatemanager.goog. 5 NS ns-cloud-c4.googledomains.com.
10.authorize.certificatemanager.goog. 5 NS ns-cloud-c1.googledomains.com.
10.authorize.certificatemanager.goog. 5 NS ns-cloud-c2.googledomains.com.
Authority
The response has no authority records.
Additional
ns-cloud-c1.googledomains.com. 5 A 216.239.32.108
ns-cloud-c2.googledomains.com. 5 A 216.239.34.108
ns-cloud-c3.googledomains.com. 5 A 216.239.36.108
ns-cloud-c4.googledomains.com. 5 A 216.239.38.108
ns-cloud-c1.googledomains.com. 5 AAAA 2001:4860:4802:32:0:0:0:6c
ns-cloud-c2.googledomains.com. 5 AAAA 2001:4860:4802:34:0:0:0:6c
ns-cloud-c3.googledomains.com. 5 AAAA 2001:4860:4802:36:0:0:0:6c
ns-cloud-c4.googledomains.com. 5 AAAA 2001:4860:4802:38:0:0:0:6c
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0