Apex domains cannot have CNAME records.
Question and response
Question
dig s3.eu-central-1.amazonaws.com. NS
Answer
s3.eu-central-1.amazonaws.com. 5 NS ns-562.awsdns-06.net.
s3.eu-central-1.amazonaws.com. 5 NS ns-321.awsdns-40.com.
s3.eu-central-1.amazonaws.com. 5 NS ns-2043.awsdns-63.co.uk.
s3.eu-central-1.amazonaws.com. 5 NS ns-1229.awsdns-25.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0