Apex domains cannot have CNAME records.
Question and response
Question
dig ontec.at. NS
Answer
ontec.at. 4 NS dns2.ontec.at.
ontec.at. 4 NS dns1.ontec.at.
Authority
The response has no authority records.
Additional
dns1.ontec.at. 4 A 37.252.250.215
dns2.ontec.at. 4 A 62.218.202.19
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0