Apex domains cannot have CNAME records.
Question and response
Question
dig fc-fra4.de. NS
Answer
fc-fra4.de. 2 NS olga.ns.cloudflare.com.
fc-fra4.de. 2 NS steven.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
olga.ns.cloudflare.com. 4 A 108.162.192.137
olga.ns.cloudflare.com. 4 A 172.64.32.137
olga.ns.cloudflare.com. 4 A 173.245.58.137
steven.ns.cloudflare.com. 4 A 108.162.195.17
steven.ns.cloudflare.com. 4 A 162.159.44.17
steven.ns.cloudflare.com. 4 A 172.64.35.17
olga.ns.cloudflare.com. 4 AAAA 2606:4700:50:0:0:0:adf5:3a89
olga.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c089
olga.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:2089
steven.ns.cloudflare.com. 4 AAAA 2606:4700:58:0:0:0:a29f:2c11
steven.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c311
steven.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:2311
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0