Apex domains cannot have CNAME records.
Question and response
Question
dig centerasecurity.dk. NS
Answer
centerasecurity.dk. 1 NS curt.ns.cloudflare.com.
centerasecurity.dk. 1 NS hera.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0