Thanks for your explanation.

I didn't have in mind the scenario of a keyboard logging user inputs besides the normal functionality of WhatsApp. I find this theory to be very plausible. Not at all happy with Meta's privacy policy, but I agree that it is worth considering other threats.

From using a VPN that logs all incoming and outgoing traffic (NetGuard) on an Android One device, I've noticied that the default Google keyboard gets in touch way too many times with some distant servers. Whereas, an open source keyboard from F-Droid, FlorisBoard, does no snooping and gets updated solely through the app store.