Apex domains cannot have CNAME records.
Question and response
Question
dig tljzshvwok.acm-validations.aws. NS
Answer
tljzshvwok.acm-validations.aws. 5 NS ns-1788.awsdns-31.co.uk.
tljzshvwok.acm-validations.aws. 5 NS ns-570.awsdns-07.net.
tljzshvwok.acm-validations.aws. 5 NS ns-461.awsdns-57.com.
tljzshvwok.acm-validations.aws. 5 NS ns-1312.awsdns-36.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0