[m-app]

Something along those lines is actually highlighted for Private Relay connections:

“All connections that use Private Relay validate that the client is an iPhone, iPad, or Mac and that the customer has a valid iCloud+ subscription. Private Relay enforces several anti-abuse and anti-fraud techniques, such as single-use authentication tokens and rate-limiting. This is designed to ensure only valid Apple devices and accounts in good standing are allowed to use Private Relay.”

https://developer.apple.com/support/prepare-your-network-for...