Apex domains cannot have CNAME records.
Question and response
Question
dig ventari.de. NS
Answer
ventari.de. 3 NS ns-cloud-a1.googledomains.com.
ventari.de. 3 NS ns-230.awsdns-28.com.
ventari.de. 3 NS ns-1846.awsdns-38.co.uk.
ventari.de. 3 NS ns-cloud-a2.googledomains.com.
Authority
The response has no authority records.
Additional
ns-cloud-a1.googledomains.com. 3 A 216.239.32.106
ns-cloud-a2.googledomains.com. 3 A 216.239.34.106
ns-cloud-a1.googledomains.com. 3 AAAA 2001:4860:4802:32:0:0:0:6a
ns-cloud-a2.googledomains.com. 3 AAAA 2001:4860:4802:34:0:0:0:6a
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0