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