Apex domains cannot have CNAME records.
Question and response
Question
dig t-systems.at. NS
Answer
t-systems.at. 5 NS dns.tsadns.eu.
t-systems.at. 5 NS ns1.anydns.cloud.
t-systems.at. 5 NS dns.t-systems.at.
Authority
The response has no authority records.
Additional
dns.tsadns.eu. 5 A 212.31.88.120
dns.t-systems.at. 5 A 212.31.86.120
dns.t-systems.at. 5 AAAA 2001:9d0:0:1:0:0:0:120
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0