I had thought that 5+ years ago, Google, Apple, Meta, etc. all created "master" private keys that would allow them to unencrypt users' data. At the time, the argument used was to combat CSA material/trafficking. I could be wrong, though. I'll try looking it up later.
Edit:
I did a quick search while on break at work.
Apple claims they have no master key and do not allow governments direct access to their servers. They only provide data when legally required to;
So it seems that Meta is likely scanning content before the encryption takes place. So they can still claim that messages are indeed E2EE, but that's useless when their AI tools are still scanning the content beforehand.
In spite of these processes, Meta has concerns. The blog post said, “Without ownership of both clients (endpoints) we cannot guarantee what a third-party provider does with sent or received messages” and thus cannot assure that messages are safely encrypted and protected. Further they said that with interoperability they would “lose connection level signals that are important for keeping users safe from spam and scams such as TCP fingerprints.”
Finally, Meta said that having a intermediary between third party provider and a Meta server could expose the “chat metadata to the proxy server, which increases the likelihood that this data could be accidentally or intentionally leaked.”
I think trusting Meta's (or Google's) E2EE at any point would have been a bad decision. Facebook thrived on collecting user data, and end-to-end encryption of private conversations spits in the face of that. If it's antithetical to their profits, there's incentive to bypass the intent but still technically be implementing it (on-device keyword scanning, maybe?).
The article says Apple is opposed. Additionally, they've already offered E2E backups, but you had to opt in. Well know they've capitulated if/when they remove that option.
In response to the order, Apple is expected to simply stop offering Advanced Data Protection in the UK. This wouldn’t meet the UK’s demand for access to files shared by global users, however.