Apex domains cannot have CNAME records.
Question and response
Question
dig adversus.dk. NS
Answer
adversus.dk. 5 NS ns1.dlx.dk.
adversus.dk. 5 NS ns2.dlx.dk.
Authority
The response has no authority records.
Additional
ns1.dlx.dk. 4 A 46.30.121.210
ns2.dlx.dk. 4 A 185.208.212.124
ns1.dlx.dk. 4 AAAA 2a00:1b18:1337:1337:0:0:0:53
ns2.dlx.dk. 4 AAAA 2a00:1b19:1337:1337:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0