Apex domains cannot have CNAME records.
Question and response
Question
dig oru.edu.gr. NS
Answer
oru.edu.gr. 5 NS faye.ns.cloudflare.com.
oru.edu.gr. 5 NS grant.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0