Apex domains cannot have CNAME records.
Question and response
Question
dig ghostdns.de. NS
Answer
ghostdns.de. 4 NS ns3.ghostdns.de.
ghostdns.de. 4 NS ns1.ghostdns.de.
ghostdns.de. 4 NS ns2.ghostdns.de.
Authority
The response has no authority records.
Additional
ns1.ghostdns.de. 4 A 94.249.135.30
ns2.ghostdns.de. 4 A 94.249.130.102
ns3.ghostdns.de. 4 A 95.215.35.254
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0