Apex domains cannot have CNAME records.
Question and response
Question
dig open-telekom-cloud.com. NS
Answer
open-telekom-cloud.com. 5 NS ns2.open-telekom-cloud.com.
open-telekom-cloud.com. 5 NS ns1.open-telekom-cloud.com.
Authority
The response has no authority records.
Additional
ns1.open-telekom-cloud.com. 5 A 80.158.48.19
ns2.open-telekom-cloud.com. 5 A 93.188.242.252
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0