Apex domains cannot have CNAME records.
Question and response
Question
dig microsoftonline.com. NS
Answer
microsoftonline.com. 5 NS ns4-38.azure-dns.info.
microsoftonline.com. 5 NS ns3-38.azure-dns.org.
microsoftonline.com. 5 NS ns1-38.azure-dns.com.
microsoftonline.com. 5 NS ns2-38.azure-dns.net.
Authority
The response has no authority records.
Additional
ns2-38.azure-dns.net. 3 A 150.171.16.38
ns3-38.azure-dns.org. 3 A 13.107.222.38
ns4-38.azure-dns.info. 3 A 13.107.206.38
ns2-38.azure-dns.net. 3 AAAA 2620:1ec:8ec:10:0:0:0:26
ns3-38.azure-dns.org. 3 AAAA 2a01:111:4000:10:0:0:0:26
ns4-38.azure-dns.info. 3 AAAA 2620:1ec:bda:10:0:0:0:26
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0