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
It's bullshit all the way down.
Are there any companies left offering free DNS usable from Terraform that aren't part of the "Internet Five Eyes"?
edit: looks like Linode may be the next best 'not terrible' option