Should be easy enough. But, the problem is the scale. I work at a privacy conscious EU based startup and we used to use quad9 for our infra. Shortly after we started using, we started to hit scalability issues. When the whole eu traffic was hot, our DNS query latency would also go up. To be able to keep up, we had to switch back to CF and Google. Hope there is a really good alternative one day.

Run your own resolver. It's not that hard.

Sure thing, but essentially it would be another thing that we have to make sure that it is protected and performant. At the time of building a startup, that’s still an item we are leaving someone else to manage.

It's simple to setup a resolver, really. Basically just "apt install unbound" and you have a resolver ready.

the only thing you might have to adjust is the access control

https://www.linuxbabe.com/ubuntu/set-up-unbound-dns-resolver...

      access-control: 10.0.0.0/8 allow
      access-control: 127.0.0.1/24 allow
      access-control: 2001:DB8::/64 allow