Apex domains cannot have CNAME records.
Question and response
Question
dig dg-w.de. NS
Answer
dg-w.de. 5 NS dnsauth002.dg-w.de.
dg-w.de. 5 NS dnsauth001.dg-w.de.
Authority
The response has no authority records.
Additional
dnsauth001.dg-w.de. 5 A 185.22.142.3
dnsauth002.dg-w.de. 5 A 94.31.64.49
dnsauth001.dg-w.de. 5 AAAA 2a00:6020:0:30:0:0:0:3
dnsauth002.dg-w.de. 5 AAAA 2a03:fc0:0:0:0:0:0:0
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0