Apex domains cannot have CNAME records.
Question and response
Question
dig mcb.dk. NS
Answer
mcb.dk. 5 NS ns3.mcb.dk.
mcb.dk. 5 NS ns2.mcb.dk.
mcb.dk. 5 NS ns1.mcb.dk.
Authority
The response has no authority records.
Additional
ns1.mcb.dk. 5 A 178.23.177.69
ns2.mcb.dk. 5 A 195.182.36.51
ns3.mcb.dk. 5 A 185.208.212.121
ns1.mcb.dk. 5 AAAA 2a00:1cf0:0:9:0:0:0:69
ns2.mcb.dk. 5 AAAA 2a00:1cf0:0:5:0:0:0:3
ns3.mcb.dk. 5 AAAA 2a00:1b19:2:1:0:0:0:121
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0