Apex domains cannot have CNAME records.
Question and response
Question
dig pdns.tech. NS
Answer
pdns.tech. 2 NS ns-76.awsdns-09.com.
pdns.tech. 2 NS ns-1553.awsdns-02.co.uk.
pdns.tech. 2 NS ns-1201.awsdns-22.org.
pdns.tech. 2 NS ns-831.awsdns-39.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0