Apex domains cannot have CNAME records.
Question and response
Question
dig d39s.de. NS
Answer
d39s.de. 5 NS adel.ns.cloudflare.com.
d39s.de. 5 NS rustam.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
adel.ns.cloudflare.com. 4 A 108.162.192.55
adel.ns.cloudflare.com. 4 A 172.64.32.55
adel.ns.cloudflare.com. 4 A 173.245.58.55
rustam.ns.cloudflare.com. 4 A 108.162.195.148
rustam.ns.cloudflare.com. 4 A 162.159.44.148
rustam.ns.cloudflare.com. 4 A 172.64.35.148
adel.ns.cloudflare.com. 4 AAAA 2606:4700:50:0:0:0:adf5:3a37
adel.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c037
adel.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:2037
rustam.ns.cloudflare.com. 4 AAAA 2606:4700:58:0:0:0:a29f:2c94
rustam.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c394
rustam.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:2394
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0