Apex domains cannot have CNAME records.
Question and response
Question
dig tfc.cz. NS
Answer
tfc.cz. 3 NS sns.cybersales.cz.
tfc.cz. 3 NS ns.cybersales.cz.
Authority
The response has no authority records.
Additional
ns.cybersales.cz. 3 A 217.11.251.228
sns.cybersales.cz. 3 A 82.208.29.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0