Apex domains cannot have CNAME records.
Question and response
Question
dig publicsherpa.com. NS
Answer
publicsherpa.com. 5 NS ns-1379.awsdns-44.org.
publicsherpa.com. 5 NS ns-209.awsdns-26.com.
publicsherpa.com. 5 NS ns-590.awsdns-09.net.
publicsherpa.com. 5 NS ns-1623.awsdns-10.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0