Apex domains cannot have CNAME records.
Question and response
Question
dig trustpilot.com. NS
Answer
trustpilot.com. 4 NS ns-1859.awsdns-40.co.uk.
trustpilot.com. 4 NS ns-1198.awsdns-21.org.
trustpilot.com. 4 NS ns-507.awsdns-63.com.
trustpilot.com. 4 NS ns-627.awsdns-14.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0