Doesn’t mean it has been hacked or their own employees able to unencrypted data. On the contrary, governments like Iran or Russia tried to ban telegram, since they wouldn’t unencrypt their data. You never hear any complaints from governments about WhatsApp for example, what has a much larger user base and is allegedly end to end encrypted. Yes, sending sensitive information should only be done via private chat, their end to end encrypted message tech. Storing the data in the server has its advantages like accessing all the data from multiple devices.

Up until some time ago, telegram has been funded by Pavel Durov, nowadays it’s funded by a premium tier that unlocks extra features.

It is the messenger with the most features that I know of