r/tv_bunny has a lot of good UK downloads. I use it mainly to watch QI :p

https://addons.mozilla.org/en-US/firefox/addon/bypass-paywalls-clean-d/

Yes. Depends on the platform. For example with Netflix L1 is required for full HD, L3 will only give you access to SD content.

Method should still work for L3 decryption. L1 decryption is hardware based instead of software based and afaik not possible to crack yet.

During cdm dumping the functions within are hooked, so while decrypting video, the private key can be extracted.

On Android this is easiest because automatic scripts exist and you can rather easily get root access.

I download audio and video to seperate files, decrypt the files and then remux together…

That would work. For example I download on my laptop but decrypt using a key/cdm from my tablet.

This still works for me: https://github.com/medvm/widevine_keys

Only thing is you need a valid, non blocked CDM. But if you have a rooted android device you can dump that with: https://github.com/wvdumper/dumper