Appreciate this deep dive on the costs to provide secure and private chat from an org I whole-heartedly support: Signal. They even dig into some of their unique privacy-preserving techniques, eg hiding GIF search terms (Meta aquired Giphy, getting a bunch of data before selling it on to Shutterstock! Now your info is owned by three companies!)
In this era of expanding consolidation, you never know where your data may end up. The only winning move for services that care about your privacy is to not collect any sensitive data in the first place.