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