Apex domains cannot have CNAME records.
Question and response
Question
dig xn--brgermeldungen-gsb.de. NS
Answer
xn--brgermeldungen-gsb.de. 5 NS ns3.futureweb.at.
xn--brgermeldungen-gsb.de. 5 NS ns2.futureweb.at.
xn--brgermeldungen-gsb.de. 5 NS ns1.futureweb.at.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0