You can also watch pretty much anything on a "rooted" computer (i.e. one where the user has admin access). I'm not entirely sure why phones are the one device where that's somehow considered a big deal.
No you don't. Safari doesn't support Widevine at all for example.
Including Widevine. Widevine Level 3 is a software based solution that can be used on a variety of platforms, but the space for Widevine Level 1 requires OS and hardware integration (which doesn't include Windows for example, but is available for Android if the OEM does the requisite work).
Server side Netflix has nothing to do, just send out the encrypted stream if asked by a client.
(Netflix do the same thing on MacOS with Apple signed drivers, backed up by hardware based security.)