Hey @shawncplus! I'm trying to do the same thing, but I'm confused about your answer.
I have a domain on namecheap, and it (website.com) points to github pages. I want to create a subdomain (subdomain.website.com) on namecheap and point it to a Digital Ocean droplet.
In my namecheap, I have:
@ - 18.104.22.168 - A(Address)
@ - 22.214.171.124 - A(Address)
www - mywebsite.com. - CNAME(Alias)
On my digitalocean:
Under the DNS, I created a dev.mywebsite.com and if you click on 'View,' I kept the default @A record with the droplet's IP and the three default NS1.DIGITALOCEAN.COM. rows.