Apex domains cannot have CNAME records.
Question and response
Question
dig porthus.com. NS
Answer
porthus.com. 5 NS ns-107.awsdns-13.com.
porthus.com. 5 NS ns-940.awsdns-53.net.
porthus.com. 5 NS ns-1044.awsdns-02.org.
porthus.com. 5 NS ns-2046.awsdns-63.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0