Apex domains cannot have CNAME records.
Question and response
Question
dig rbgk.raiffeisen.at. NS
Answer
rbgk.raiffeisen.at. 5 NS ns0155.secondary.cloudflare.com.
rbgk.raiffeisen.at. 5 NS ns0094.secondary.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0