Yes, quad9 is a DNS provider, meaning the way to configure quad9 as your DNS provider is the same as configuring cloudflare but instead of 1.1.1.1 it’s 9.9.9.9 (hence the name quad9)

edit: if you’re using android or a browser (or really anything that uses DNS over https), the URLs are different, but you can find more info at https://quad9.net/

I use duckduckgo on Firefox and mullvad browser, I also use it on my phones, but in my ungoogled chromium I’m trying out startpage.

I choose linux because:

1. Installing a programming language doesn’t require setting up a path, the package manager does it automatically.
2. It’s 100x easier to be private on linux than on Windows or macOS.
3. There’s no AI in the notepad app.
4. It just works.