None on ARM. Google never offered widevine to Firefox on ARM64.

Exactly, AFAIK you can't watch netflix on your ARM SBC.

You can, all you need to do is to extract the widevine binary from a ChromeOS arm build and put them on your Pi/ARM board.

Admittedly, it's a bit cumbersome to do this, but it works very well. I've been watching Netflix on my Raspberry Pi 4 for over a year using it.

Also, according to this guy [0] you now seem to be able to just install libwidevine in Raspberry OS. I haven't tested this yet though.

[0]: https://lemariva.com/blog/2021/04/raspberry-pi-amazon-prime-...

Right, as long as you are using Chrome (maybe chromium in a 32 bit chroot or container if you do not have an RPI), you can use widevine. But I'm not a big fan of the RPI devices, or chrome.

4k Netflix doesn't work on Linux, and also downloading for offline viewing, but I think those only work on Windows with HDCP enabled.