Apex domains cannot have CNAME records.
Question and response
Question
dig vitkovice.cz. NS
Answer
vitkovice.cz. 5 NS ns2.vitkovice.cz.
vitkovice.cz. 5 NS aeson.vitkovice.cz.
Authority
The response has no authority records.
Additional
ns2.vitkovice.cz. 5 A 185.252.90.21
aeson.vitkovice.cz. 5 A 176.67.229.196
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0