Apex domains cannot have CNAME records.
Question and response
Question
dig motorradundreisen.de. NS
Answer
motorradundreisen.de. 5 NS dns2.motorradundreisen.de.
motorradundreisen.de. 5 NS dns3.motorradundreisen.de.
motorradundreisen.de. 5 NS dns1.motorradundreisen.de.
Authority
The response has no authority records.
Additional
dns1.motorradundreisen.de. 5 A 192.174.68.104
dns2.motorradundreisen.de. 5 A 45.87.158.53
dns3.motorradundreisen.de. 5 A 45.87.158.53
dns1.motorradundreisen.de. 5 AAAA 2001:67c:1bc:0:0:0:0:104
dns2.motorradundreisen.de. 5 AAAA 2a02:d500:0:0:0:0:0:53
dns3.motorradundreisen.de. 5 AAAA 2a02:d500:0:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0