Apex domains cannot have CNAME records.
Question and response
Question
dig glbdns.protection.outlook.COM. NS
Answer
glbdns.protection.outlook.COM. 1 NS ns1-36.azure-dns.COM.
glbdns.protection.outlook.COM. 1 NS ns3-36.azure-dns.org.
glbdns.protection.outlook.COM. 1 NS ns2-36.azure-dns.net.
glbdns.protection.outlook.COM. 1 NS ns4-36.azure-dns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0