Apex domains cannot have CNAME records.
Question and response
Question
dig kwddbwrbjk.acm-validations.aws. NS
Answer
kwddbwrbjk.acm-validations.aws. 5 NS ns-1822.awsdns-35.co.uk.
kwddbwrbjk.acm-validations.aws. 5 NS ns-1202.awsdns-22.org.
kwddbwrbjk.acm-validations.aws. 5 NS ns-402.awsdns-50.com.
kwddbwrbjk.acm-validations.aws. 5 NS ns-771.awsdns-32.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0