Apex domains cannot have CNAME records.
Question and response
Question
dig mallorca-steuerberater.com. NS
Answer
mallorca-steuerberater.com. 5 NS ns-866.awsdns-44.net.
mallorca-steuerberater.com. 5 NS ns-1816.awsdns-35.co.uk.
mallorca-steuerberater.com. 5 NS ns-2036.awsdns-62.co.uk.
mallorca-steuerberater.com. 5 NS ns-166.awsdns-20.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0