Most industry standard software that people use in their jobs is closed source. When you watch movies or listen to music or play video games you're supporting proprietary software. Same with finance and basically any office job. Niche IT jobs are the exception but I've been in enterprise IT for 20 years and this is just how it is in a capitalist economy. I'd prefer for public ownership of technology platforms but it's basically reduced to a consumption model within the current system. Like the platforms people consume media through isn't very significant, which the open source community puts a lot of ideological importance on. Most open source projects are also abandoned and become obsolete too quickly. I've basically been relying on the same set of proprietary Adobe software for part of my income since the 90s, can't name an open source alternative that does what I need it to do or has this longevity even though I'd prefer it.

Btw a way you can verify the security of a chat app is by reading case docs from law enforcement about what's required to obtain communications through said platform. With whatsapp the closest they can get to message content is by retreiving cache from the iPhone chatsearch database, and metadata from WhatsApp about who sent a message to whom and when but not the message contents. Retrieval of WhatApp messages through proprietary security forensics software is limited to how certain phone models and OSs locally cache messages basically. This applies to different platforms the same way though and isn't something special about WhatsApp or Meta. The unique thing to Meta is how quickly they respond to law enforcement requests about metadata collection.