So I see Signal recommended instead, but one thing sticks out like a sore thumb. If it’s privacy-focused and it has a windows application, why the need for a phone to set it up?

The actual source is from Reuters: https://www.reuters.com/technology/cybersecurity/governments-spying-apple-google-users-through-push-notifications-us-senator-2023-12-06/

I don’t get it…
What is a pacer test? Is it a US specific thing?

Nah, that’s not how most cyclists are, especially not in the Netherlands.