Just a small nitpick,

> Telegram has no cross-platform E2EE

If you mean between an Android and an Apple device, that is supported, to my knowledge.

Telegram's E2EE is acceptable only for limited use cases, though, it's crippled beyond belief.

No I mean between your smartphone and desktop clients.

When you can't continue the secret chat on your desktop device, you'll eventually get tired of having to dig your phone from your phone, unlock it, open telegram, navigate to chat, reply, lock phone, put it back to pocket continue work; the alternative of ditching security and just alt-tabbing to insecure chat on desktop client wins.

This is what a modern backdoor would look like. Vendor can't be blamed about introducing a backdoor, when using the backdoor feature is your own fault.

And this is just DMs where E2EE is possible in the first place.

Ah well yes; the chat is also bound to an individual device, it's not even possible to export it without root

The only purpose of the private chats feature at this point is to be able to claim that Telegram can do E2EE