Apex domains cannot have CNAME records.
Question and response
Question
dig htb-cloud.com. NS
Answer
htb-cloud.com. 3 NS ns1.htb-cloud.com.
htb-cloud.com. 3 NS ns2.htb-cloud.com.
Authority
The response has no authority records.
Additional
ns1.htb-cloud.com. 3 A 85.9.212.197
ns2.htb-cloud.com. 3 A 85.9.195.106
ns1.htb-cloud.com. 3 AAAA 2a04:3544:1000:1510:a4ba:3bff:fe08:3221
ns2.htb-cloud.com. 3 AAAA 2605:7380:8000:1000:a4ba:3bff:fe08:31e1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0