Apex domains cannot have CNAME records.
Question and response
Question
dig access.lichtwelle.de. NS
Answer
access.lichtwelle.de. 5 NS dns2.kommitt.de.
access.lichtwelle.de. 5 NS dns1.kommitt.de.
Authority
The response has no authority records.
Additional
dns1.kommitt.de. 5 A 185.29.216.251
dns2.kommitt.de. 5 A 185.29.217.251
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0