WhatsApp by default backs up your private key to the cloud. Even if you don't do this your contacts might, which means "end-to-end encryption" is only theoretic

WhatsApp by default backs up your private key to the cloud. Even if you don't do this your contacts might, which means "end-to-end encryption" is only theoretical, and you have no idea whether it actually is. Telegram's secret chat keys are never backed up. It's also faster and more reliable than Signal. If E2EE is important to you, you can use secret chats.