Search for widevine decrypt. You’ll find code and forums where at least some L3 (software) keys are publicly shared. For high resolution on some platforms, you need L1 keys, but as far as I understand the decryption process basically stays the same once you have a working key.
You won't find a ton of up-to-date info that would let you do the same - the scene groups hold their methods closely specifically because of this cat-and-mouse game.
47282847|3 months ago
Random article: https://www.ismailzai.com/blog/picking-the-widevine-locks
Claimed to be L1 key leaks (probably all blacklisted by now): https://github.com/Mavrick102/WIDEVINE-CDM-L1-Giveaway
sodality2|3 months ago