Apex domains cannot have CNAME records.
Question and response
Question
dig dnsx1.pl. NS
Answer
dnsx1.pl. 1 NS ns1.dnsx1.pl.
dnsx1.pl. 1 NS ns3.dnsx1.pl.
dnsx1.pl. 1 NS ns2.dnsx1.pl.
Authority
The response has no authority records.
Additional
ns1.dnsx1.pl. 1 A 96.45.80.1
ns2.dnsx1.pl. 1 A 46.31.236.1
ns3.dnsx1.pl. 1 A 43.247.170.1
ns1.dnsx1.pl. 1 AAAA 2600:180a:1001:0:0:0:0:1
ns2.dnsx1.pl. 1 AAAA 2600:180b:2001:0:0:0:0:1
ns3.dnsx1.pl. 1 AAAA 2600:180c:3001:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0