IMO "end-to-end encryption" simply isn't possible when the application is run by the same company as the servers the data sits on, is closed source, and can at any time, see the decrypted contents of data it downloads from their servers and do whatever they want with it.
Same issue with Proton, MEGA, and any other e2ee app... it's only useful when the company decides not to mess with the data it could always decrypt locally. Also why people are hesitant to use javascript-based e2ee solutions where the site owner can modify the code at will to do what they want.
This is based on a faulty understanding of the underlying systems. The risk with this sort of E2E encryption is not that the service provider pinky promises not to decrypt what they have, it's that they promise they will not insert a new key into your circle of trust to subsequently start decrypting things.
Only if the company misleads and adds a backdoor to the front-end app (thus this entire discussion).
If the company is misleading, any encryption technology is irrelevant anyway.
There's no issue with mega. There are third party apps and as long as you don't login to mega.nz with their website you're fine. And they also have SDK you can use that they'll not be able to control/manipulate without your knowledge.
Beyond the privacy marketing angle, e2e allows companies with global exposure to sidestep any unpleasantness when they get a subpoena from Bumfuck, Nowhere.
Sure, the NSA, GCHQ and Mossad have a way to exfiltrate the unencrypted data but proprietary e2e is a good thing for most people IMO. Shifts the risk from "my messages are theoretically available to most law enforcement in the globe" to "YOU’RE STILL GONNA BE MOSSAD’ED UPON"[0]. This is specially good for me because I know the equivalent to the FBI where is live is too cheap to buy a Cellebrite [1] license.
[0] https://www.usenix.org/system/files/1401_08-12_mickens.pdf [1] https://arstechnica.com/gadgets/2025/10/leaker-reveals-which...
EDIT: I suppose someone could ask about Meta. The reason behind their support for scanning (and removing e2e in facebook msg) is simply regulatory capture. The zucc wishes to have a letter of marque to "protect" your children and remove the "unsafe" competitors.
EDIT2: Used the wrong term, I mixed up exfiltration channel with sidechannel attack.