If you scrolled down in the link provided above, it mentions with BOTH Standard and Advanced data protection messages are end to end encrypted, it’s just with advanced data protection the encryption key also ends up being encrypted too, but I’m positive even this has changed recently. You can try looking at logs when you turn on messages in iCloud and see that your messages are encrypted.

So lots of confusion in this thread, my advice for Apple would be make it very very clear to users that your data is safe. I mean they are threatening to back out of UK, so it’s against their core principles and also probably very technically expensive to undo they end to end encrypted system.