Apex domains cannot have CNAME records.
Question and response
Question
dig castle-it.net. NS
Answer
castle-it.net. 5 NS dns2.castle-it.net.
castle-it.net. 5 NS dns1.castle-it.net.
Authority
The response has no authority records.
Additional
dns1.castle-it.net. 5 A 185.88.198.4
dns2.castle-it.net. 5 A 185.88.198.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0