Apex domains cannot have CNAME records.
Question and response
Question
dig cname.vercel-dns.com. NS
Answer
cname.vercel-dns.com. 5 NS ns4.vercel-dns-3.com.
cname.vercel-dns.com. 5 NS ns3.vercel-dns-3.com.
cname.vercel-dns.com. 5 NS ns1.vercel-dns-3.com.
cname.vercel-dns.com. 5 NS ns2.vercel-dns-3.com.
Authority
The response has no authority records.
Additional
ns1.vercel-dns-3.com. 5 A 205.251.193.92
ns2.vercel-dns-3.com. 5 A 205.251.194.149
ns3.vercel-dns-3.com. 5 A 205.251.197.116
ns4.vercel-dns-3.com. 5 A 205.251.199.60
ns1.vercel-dns-3.com. 5 AAAA 2600:9000:5301:5c00:0:0:0:1
ns2.vercel-dns-3.com. 5 AAAA 2600:9000:5302:9500:0:0:0:1
ns3.vercel-dns-3.com. 5 AAAA 2600:9000:5305:7400:0:0:0:1
ns4.vercel-dns-3.com. 5 AAAA 2600:9000:5307:3c00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0