Apex domains cannot have CNAME records.
Question and response
Question
dig Materna.DE. NS
Answer
materna.de. 5 NS ns1.domaindiscount24.net.
materna.de. 5 NS ns3.domaindiscount24.net.
materna.de. 5 NS mcn-ext-dns-2.materna.de.
Authority
The response has no authority records.
Additional
mcn-ext-dns-2.materna.de. 5 A 3.123.207.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0