Apex domains cannot have CNAME records.
Question and response
Question
dig tfmgdnztqk.acm-validations.aws. NS
Answer
tfmgdnztqk.acm-validations.aws. 5 NS ns-1739.awsdns-25.co.uk.
tfmgdnztqk.acm-validations.aws. 5 NS ns-219.awsdns-27.com.
tfmgdnztqk.acm-validations.aws. 5 NS ns-719.awsdns-25.net.
tfmgdnztqk.acm-validations.aws. 5 NS ns-1356.awsdns-41.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0