Apex domains cannot have CNAME records.
Question and response
Question
dig mhbtsbpdnt.acm-validations.aws. NS
Answer
mhbtsbpdnt.acm-validations.aws. 5 NS ns-764.awsdns-31.net.
mhbtsbpdnt.acm-validations.aws. 5 NS ns-1698.awsdns-20.co.uk.
mhbtsbpdnt.acm-validations.aws. 5 NS ns-183.awsdns-22.com.
mhbtsbpdnt.acm-validations.aws. 5 NS ns-1306.awsdns-35.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0