The loophole in WhatsApp's end-to-end encryption is simple: The recipient of any WhatsApp message can flag it. Once flagged, the message is copied on the recipient's device and sent as a separate message to Facebook for review.
That practically applies to every form of digital communication. Sender/recipient has it on their end unencrypted and passes/leaks it on elsewhere
Really I don't know but I remember dealing with a dual vpn years ago with Samsung phones
https://docs.samsungknox.com/dev/knox-sdk/features/mdm-providers/vpn/vpn-chaining/