Apex domains cannot have CNAME records.
Question and response
Question
dig izernet.pl. NS
Answer
izernet.pl. 5 NS dns13.ovh.net.
izernet.pl. 5 NS ns13.ovh.net.
Authority
The response has no authority records.
Additional
ns13.ovh.net. 3 A 5.39.112.241
dns13.ovh.net. 3 A 5.135.98.29
ns13.ovh.net. 3 AAAA 2001:41d0:b00:ec00:0:0:0:2
dns13.ovh.net. 3 AAAA 2001:41d0:d00:f200:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0