I am shocked at how many people watch Netflix in their browser. I have multiple different ways (AppleTV, Xbox, TV Smart App) to watch Netflix on my tv, and at least 2 of them support 4k.
Most people don't realize this but you can only watch Netflix in 4K in a browser if you're using Microsoft Edge on Windows or Safari in macOS 11. In fact, you can only get 1080p if you're running Chrome in Chrome OS, or IE, or Safari. All other browsers, including Chrome and FF on macOS, Linux, and Windows, are stuck at 720p.
Their blog post[0] from 2017 sounded hopeful for higher resolution video on Linux - they wrote "We... look forward to high-resolution video being available on more platforms soon" almost immediately after announcing FF on Linux was supported - but in hindsight it's clear that what they really meant was what you point out - support for things like Apple TV, Xbox, and TV Smart Apps.
[0]: https://netflixtechblog.com/update-on-html5-video-for-netfli...
Edge hasn't been around as long as Netflix has provided in-browser service, I'd have thought Chrome w/ Widevine would have been part of Netflix' success.
And of course because I’m on Linux I can’t get even 1080p encoded at a shitty bitrate unless I force it with a Firefox extension that they can gimp at any time (in a way, many thanks to the engineers who made the extension possible by relaxing checks on the browser).
I don’t understand why most platforms hate their paying users like this - I can and will pirate a Blu-ray quality rip if I can’t pay for it easily.
They don't. They're just very noisy.