Apex domains cannot have CNAME records.
Question and response
Question
dig osr-rohstoffe.de. NS
Answer
osr-rohstoffe.de. 4 NS mariah.ns.cloudflare.com.
osr-rohstoffe.de. 4 NS nikon.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
nikon.ns.cloudflare.com. 4 A 108.162.195.176
nikon.ns.cloudflare.com. 4 A 162.159.44.176
nikon.ns.cloudflare.com. 4 A 172.64.35.176
mariah.ns.cloudflare.com. 4 A 108.162.194.200
mariah.ns.cloudflare.com. 4 A 162.159.38.200
mariah.ns.cloudflare.com. 4 A 172.64.34.200
nikon.ns.cloudflare.com. 4 AAAA 2606:4700:58:0:0:0:a29f:2cb0
nikon.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c3b0
nikon.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:23b0
mariah.ns.cloudflare.com. 4 AAAA 2606:4700:50:0:0:0:a29f:26c8
mariah.ns.cloudflare.com. 4 AAAA 2803:f800:50:0:0:0:6ca2:c2c8
mariah.ns.cloudflare.com. 4 AAAA 2a06:98c1:50:0:0:0:ac40:22c8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0