Apex domains cannot have CNAME records.
Question and response
Question
dig semiro.de. NS
Answer
semiro.de. 2 NS ns-cloud-b2.googledomains.com.
semiro.de. 2 NS ns-cloud-b1.googledomains.com.
semiro.de. 2 NS ns-1518.awsdns-61.org.
semiro.de. 2 NS ns-1962.awsdns-53.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0