[Cthulhu_]

> You would assume macOS as the operating system, but is that manageable at that scale?

Sure, it's a unix system. You can go far with SSHing into a machine and running some commands. Also, they only very recently discontinued MacOS Server (https://support.apple.com/en-us/HT208312)

Hardware-wise, it's either a battery of Mac Minis or Mac Pros, or maybe they've made custom hardware so they can put Apple hardware in a blade server form factor.