Apex domains cannot have CNAME records.
Question and response
Question
dig geekbyte.de. NS
Answer
geekbyte.de. 2 NS second-dns.netcup.net.
geekbyte.de. 2 NS root-dns.netcup.net.
geekbyte.de. 2 NS third-dns.netcup.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0