Apex domains cannot have CNAME records.
Question and response
Question
dig st-poelten.at. NS
Answer
st-poelten.at. 5 NS ns80.kabelplus.at.
st-poelten.at. 5 NS ns81.kabelplus.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0