Apex domains cannot have CNAME records.
Question and response
Question
dig nono.io. NS
Answer
nono.io. 5 NS ns-he.nono.io.
nono.io. 5 NS ns-vultr.nono.io.
Authority
The response has no authority records.
Additional
ns-he.nono.io. 5 A 78.46.204.247
ns-vultr.nono.io. 5 A 158.247.194.13
ns-he.nono.io. 5 AAAA 2a01:4f8:c17:b8f:0:0:0:2
ns-vultr.nono.io. 5 AAAA 2401:c080:1c00:29d6:0:0:0:0
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0