Apex domains cannot have CNAME records.
Question and response
Question
dig demo5.de. NS
Answer
demo5.de. 5 NS ns1.demo5.de.
demo5.de. 5 NS ns2.demo5.de.
Authority
The response has no authority records.
Additional
ns1.demo5.de. 5 A 5.9.117.74
ns2.demo5.de. 5 A 188.34.201.30
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0