Apex domains cannot have CNAME records.
Question and response
Question
dig yssrbzrnkq.acm-validations.aws. NS
Answer
yssrbzrnkq.acm-validations.aws. 5 NS ns-1879.awsdns-42.co.uk.
yssrbzrnkq.acm-validations.aws. 5 NS ns-816.awsdns-38.net.
yssrbzrnkq.acm-validations.aws. 5 NS ns-119.awsdns-14.com.
yssrbzrnkq.acm-validations.aws. 5 NS ns-1497.awsdns-59.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0