Apex domains cannot have CNAME records.
Question and response
Question
dig iserver.si. NS
Answer
iserver.si. 5 NS mckinley.ns.cloudflare.com.
iserver.si. 5 NS konnor.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0