Comment by mnordhoff

I have bad news for you, Linode's authoritative DNS service also uses Cloudflare DNS Firewall.

  $ dig +short ns1.digitalocean.com aaaa
  2400:cb00:2049:1::adf5:3a33
  $ dig +short ns1.linode.com aaaa
  2400:cb00:2049:1::a29f:1a63