Apex domains cannot have CNAME records.
Question and response
Question
dig data-cross.de. NS
Answer
data-cross.de. 5 NS ns01.kraemer-it.cloud.
data-cross.de. 5 NS ns02.kraemer-it.cloud.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0