To clarify because this is always a point of confusion whenever the topic comes up. Telegram is, of course, transport encrypted. Someone listening on the wire cannot read your data. It is not end-to-end encrypted, meaning Telegram can always read your messages and can, in principle, give anyone access.
Lovely, the parent comment mentioned blockchain but was since edited… Trust me I would not have brought it up otherwise.
Blockchains have the property of being append-only, so a blockchain is precisely what makes it impossible to delete transactions. That being said, in a distributed system, once the message leaves trusted servers, it is obviously also impossible to delete it.
Thanks for the clarification I should have mentioned this. Especially for calls it is actually relevant but I feel like very few people actually use secret chats.