Apex domains cannot have CNAME records.
Question and response
Question
dig social.cz. NS
Answer
social.cz. 5 NS meadow.ns.cloudflare.com.
social.cz. 5 NS kobe.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0