Apex domains cannot have CNAME records.
Question and response
Question
dig oci.oraclecloud.com. NS
Answer
oci.oraclecloud.com. 2 NS a4-67.akam.net.
oci.oraclecloud.com. 2 NS ns3.p200.dns.oraclecloud.net.
oci.oraclecloud.com. 2 NS a13-64.akam.net.
oci.oraclecloud.com. 2 NS ns1.p200.dns.oraclecloud.net.
oci.oraclecloud.com. 2 NS ns2.p200.dns.oraclecloud.net.
oci.oraclecloud.com. 2 NS ns4.p200.dns.oraclecloud.net.
oci.oraclecloud.com. 2 NS a1-143.akam.net.
oci.oraclecloud.com. 2 NS a7-64.akam.net.
oci.oraclecloud.com. 2 NS ns.us-phoenix-1.dns.oraclerealm1.com.
oci.oraclecloud.com. 2 NS a6-66.akam.net.
oci.oraclecloud.com. 2 NS a18-65.akam.net.
Authority
The response has no authority records.
Additional
a6-66.akam.net. 1 A 23.211.133.66
a6-66.akam.net. 1 AAAA 2600:1401:1:0:0:0:0:42
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0