Apex domains cannot have CNAME records.
Question and response
Question
dig windows.net. NS
Answer
windows.net. 5 NS ns4-39.azure-dns.info.
windows.net. 5 NS ns1-39.azure-dns.com.
windows.net. 5 NS ns2-39.azure-dns.net.
windows.net. 5 NS ns3-39.azure-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0