Apex domains cannot have CNAME records.
Question and response
Question
dig antagus.de. NS
Answer
antagus.de. 5 NS ns1.antagus.de.
antagus.de. 5 NS ns2.antagus.de.
Authority
The response has no authority records.
Additional
ns1.antagus.de. 5 A 195.191.92.10
ns2.antagus.de. 5 A 195.191.93.10
ns1.antagus.de. 5 AAAA 2001:67c:2394:1:0:0:0:1001
ns2.antagus.de. 5 AAAA 2001:67c:2394:3:0:0:0:1001
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0