What are the verifiable privacy features macOS provides? Being tired of reading new privacy issues affecting Windows, release after release, and OEMs introducing their own privacy-breaking software (or vulnerability - such as the recent Dell remote execution bug,) I'm looking into how macOS is different. Having heard so many people talking how much Apple cares about their users privacy, whether it's macOS, Macbooks or various devices.

Is there a reliable source / list of privacy feature / officially and legally-binding privacy policy (without having to go through all the fluff) I can refer to, to form my opinion?
Apple has detailed pages describing their intent and operation. There's also an overview of the security technologies used in MacOS.

On MacOS, the main feature is FileVault (or the default encryption on the newest Macs with "T2" controller chips. Disk encryption means that the data on your Mac can only be accessed by someone with the password.
Safari has been at the fore-front of technologies to stop user tracking and maintain privacy.

On iOS, I'm sure you will have seen new reports of the US government wanting Apple to help them get into iPhones, and Apple indicating that is unable to comply, (and also unwilling). Here's Apple's iOS Security documentation.

There will always be vulnerabilities, exploits, and mistakes, of course.