Apex domains cannot have CNAME records.
Question and response
Question
dig zzxlnyslwt.acm-validations.aws. NS
Answer
zzxlnyslwt.acm-validations.aws. 5 NS ns-341.awsdns-42.com.
zzxlnyslwt.acm-validations.aws. 5 NS ns-1041.awsdns-02.org.
zzxlnyslwt.acm-validations.aws. 5 NS ns-619.awsdns-13.net.
zzxlnyslwt.acm-validations.aws. 5 NS ns-1956.awsdns-52.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0