In addition to these criteria, the following can also be attributed here: open source code, a ban on screenshots in secret chats, the presence of group E2EE chats, and so on.
Well, you should also understand a couple of important things:The presence of end-to-end encryption in the product does not at all guarantee that the correspondence will not “go” into third parties. With a very strong desire, you can bypass it, or simply exploit some internal “hole” of the messenger. We know a lot of such examples (WhatsAp, Facebook Messenger, and others).
Argus Chat 