Apex domains cannot have CNAME records.
Question and response
Question
dig sdgjtdhdhz.acm-validations.aws. NS
Answer
sdgjtdhdhz.acm-validations.aws. 5 NS ns-1871.awsdns-41.co.uk.
sdgjtdhdhz.acm-validations.aws. 5 NS ns-224.awsdns-28.com.
sdgjtdhdhz.acm-validations.aws. 5 NS ns-555.awsdns-05.net.
sdgjtdhdhz.acm-validations.aws. 5 NS ns-1137.awsdns-14.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0