Apex domains cannot have CNAME records.
Question and response
Question
dig nextflow.cloud. NS
Answer
nextflow.cloud. 5 NS ns-1940.awsdns-50.co.uk.
nextflow.cloud. 5 NS ns-1586.awsdns-06.co.uk.
nextflow.cloud. 5 NS ns-1451.awsdns-53.org.
nextflow.cloud. 5 NS ns-1982.awsdns-55.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0