Apex domains cannot have CNAME records.
Question and response
Question
dig apple.com. NS
Answer
apple.com. 5 NS a.ns.apple.com.
apple.com. 5 NS d.ns.apple.com.
apple.com. 5 NS c.ns.apple.com.
apple.com. 5 NS b.ns.apple.com.
Authority
The response has no authority records.
Additional
a.ns.apple.com. 5 A 17.253.200.1
b.ns.apple.com. 5 A 17.253.207.1
c.ns.apple.com. 5 A 204.19.119.1
d.ns.apple.com. 5 A 204.26.57.1
a.ns.apple.com. 5 AAAA 2620:149:ae0:0:0:0:0:53
b.ns.apple.com. 5 AAAA 2620:149:ae7:0:0:0:0:53
c.ns.apple.com. 5 AAAA 2620:171:800:714:0:0:0:1
d.ns.apple.com. 5 AAAA 2620:171:801:714:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0