Apex domains cannot have CNAME records.
Question and response
Question
dig schwabe.de. NS
Answer
schwabe.de. 5 NS ezra.ns.cloudflare.com.
schwabe.de. 5 NS ligia.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
ezra.ns.cloudflare.com. 3 A 108.162.195.15
ezra.ns.cloudflare.com. 3 A 162.159.44.15
ezra.ns.cloudflare.com. 3 A 172.64.35.15
ligia.ns.cloudflare.com. 3 A 108.162.194.4
ligia.ns.cloudflare.com. 3 A 162.159.38.4
ligia.ns.cloudflare.com. 3 A 172.64.34.4
ezra.ns.cloudflare.com. 3 AAAA 2606:4700:58:0:0:0:a29f:2c0f
ezra.ns.cloudflare.com. 3 AAAA 2803:f800:50:0:0:0:6ca2:c30f
ezra.ns.cloudflare.com. 3 AAAA 2a06:98c1:50:0:0:0:ac40:230f
ligia.ns.cloudflare.com. 3 AAAA 2606:4700:50:0:0:0:a29f:2604
ligia.ns.cloudflare.com. 3 AAAA 2803:f800:50:0:0:0:6ca2:c204
ligia.ns.cloudflare.com. 3 AAAA 2a06:98c1:50:0:0:0:ac40:2204
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0