Apex domains cannot have CNAME records.
Question and response
Question
dig bauma-baubeschlaege.de. NS
Answer
bauma-baubeschlaege.de. 1 NS vmd41165.contaboserver.net.
bauma-baubeschlaege.de. 1 NS pdns02.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0