Apex domains cannot have CNAME records.
Question and response
Question
dig server4you.de. NS
Answer
server4you.de. 5 NS wally.ns.cloudflare.com.
server4you.de. 5 NS matt.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0