Apex domains cannot have CNAME records.
Question and response
Question
dig regex.com. NS
Answer
regex.com. 4 NS ns6.padinet.com.
regex.com. 4 NS ns8.padinet.com.
regex.com. 4 NS ns5.padinet.com.
regex.com. 4 NS ns7.padinet.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0