Apex domains cannot have CNAME records.
Question and response
Question
dig sps-ocs.de. NS
Answer
sps-ocs.de. 5 NS ns41.infomaniak.com.
sps-ocs.de. 5 NS ns42.infomaniak.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0