Apex domains cannot have CNAME records.
Question and response
Question
dig oracle.com. NS
Answer
oracle.com. 5 NS a18-67.akam.net.
oracle.com. 5 NS a1-160.akam.net.
oracle.com. 5 NS ns1.p201.dns.oraclecloud.net.
oracle.com. 5 NS ns4.p201.dns.oraclecloud.net.
oracle.com. 5 NS ns3.p201.dns.oraclecloud.net.
oracle.com. 5 NS ns2.p201.dns.oraclecloud.net.
oracle.com. 5 NS a11-66.akam.net.
oracle.com. 5 NS a13-65.akam.net.
Authority
The response has no authority records.
Additional
a18-67.akam.net. 2 A 95.101.36.67
a18-67.akam.net. 2 AAAA 2600:1480:4800:0:0:0:0:43
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0