[a0123]

That's how successful Telegram's PR has been. People believe - like you do - that it's end to end encrypted. It's not.

The secret chats presumably are (if you trust Telegram). Secret chats are 1 to 1. So anything outside of those that most people on Telegram access (massive channels and groups, smaller groups, private groups and channels) is NOT encrypted.

[codedokode]

Sorry for whataboutism, but Apple does the same thing. It claims in advertising that all cloud backups are "encrypted", but if you dig deeper, "encrypted" means "encrypted with a key that is stored in the cloud" (see the table in [1]). Apple also (exactly like Telegram) requires you to opt-in for E2E encryption of backups, it is not enabled by default and even in this case contact list backup do not support E2E encryption.

The article claims that "Contacts and calendars are built on industry standards (CalDAV and CardDAV) that do not provide built-in support for end-to-end encryption." but it seems like a weak argument. Nobody actually cares what protocol is used between a device and a cloud.

[1] https://support.apple.com/en-us/102651