Apex domains cannot have CNAME records.
Question and response
Question
dig dataforest-intern.de. NS
Answer
dataforest-intern.de. 4 NS alaric.ns.cloudflare.com.
dataforest-intern.de. 4 NS holly.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0