Apex domains cannot have CNAME records.
Question and response
Question
dig kurios.at. NS
Answer
kurios.at. 5 NS dnsirl.nico.email.
kurios.at. 5 NS zimmer73.nervenklinik.at.
kurios.at. 5 NS zimmer12.nervenklinik.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0