Apex domains cannot have CNAME records.
Question and response
Question
dig sharepoint.com. NS
Answer
sharepoint.com. 5 NS ns3-221.azure-dns.org.
sharepoint.com. 5 NS ns2-221.azure-dns.net.
sharepoint.com. 5 NS ns1-221.azure-dns.com.
sharepoint.com. 5 NS ns4-221.azure-dns.info.
Authority
The response has no authority records.
Additional
ns2-221.azure-dns.net. 3 A 150.171.21.221
ns3-221.azure-dns.org. 3 A 204.14.183.221
ns4-221.azure-dns.info. 3 A 208.84.5.221
ns2-221.azure-dns.net. 3 AAAA 2620:1ec:8ec:700:0:0:0:dd
ns3-221.azure-dns.org. 3 AAAA 2a01:111:4000:700:0:0:0:dd
ns4-221.azure-dns.info. 3 AAAA 2620:1ec:bda:700:0:0:0:dd
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0