WhatsApp does use that same Signal protocol for its messages but that's very poor writing considering all the tracked metadata arguably makes it just as insecure as Telegram.
So the Hunter Biden case is a complete farce but I found it alarming that they were proving WhatsApp messages as evidence during the trial. Clearly the messages aren't encrypted against Meta, or they hold keys users don't know about or they wouldn't be able to furnish messages.
I might be missing the point, but isn’t this a decently dumbed-down description of the difference between services that are end-to-end encrypted and those that are not?