Apex domains cannot have CNAME records.
Question and response
Question
dig eu-south-1.compute.amazonaws.com. NS
Answer
eu-south-1.compute.amazonaws.com. 5 NS ns-678.awsdns-20.net.
eu-south-1.compute.amazonaws.com. 5 NS ns-1236.awsdns-26.org.
eu-south-1.compute.amazonaws.com. 5 NS ns-1548.awsdns-01.co.uk.
eu-south-1.compute.amazonaws.com. 5 NS ns-189.awsdns-23.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0