I'm using AWS Route 53 to manage my apex domain (I cannot move the apex to Vercel due to external factors), and I'd like Vercel to manage the DNS on a subdomain on it instead so that I can easily add new subdomains to that subdomain via Vercel vs having to manually edit Route 53 records when I connect a new project.

I only get a "CNAME (Recommended)" option after setting TXT verification. How do I get the option to assign the Vercel nameservers to it? Not sure if it matters, but it is a ".ai" domain.

The screenshot here shows "or Nameservers" for a subdomain, which is what I'm trying to accomplish:

https://vercel.com/docs/projects/domains/add-a-domain#subdomains