Apex domains cannot have CNAME records.
Question and response
Question
dig qxcwttcyyb.acm-validations.aws. NS
Answer
qxcwttcyyb.acm-validations.aws. 5 NS ns-1133.awsdns-13.org.
qxcwttcyyb.acm-validations.aws. 5 NS ns-448.awsdns-56.com.
qxcwttcyyb.acm-validations.aws. 5 NS ns-684.awsdns-21.net.
qxcwttcyyb.acm-validations.aws. 5 NS ns-1710.awsdns-21.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0