Apex domains cannot have CNAME records.
Question and response
Question
dig mc. NS
Answer
mc. 4 NS ns3.nic.mc.
mc. 4 NS ns2.nic.mc.
mc. 4 NS mc.cctld.authdns.ripe.net.
mc. 4 NS ns1.nic.mc.
Authority
The response has no authority records.
Additional
ns1.nic.mc. 172799 A 185.243.3.205
ns2.nic.mc. 172799 A 13.36.89.111
ns3.nic.mc. 172799 A 15.237.153.29
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0