That was a rhetorical qustion. It’s their servers which generates the key. So Telegram has both the lock and the key and claim they are “heavily encrypted”.

Signal or SimpleX.

All data sent to Telegram’s servers will be encrypted once they reach the servers.

and who generated the key?

Every text you send through Telegram is stored in plaintext. Telegram and authorities can access that without your knowledge. Also it will get leaked in a breach someday.

Now you decide for yourself if it’s private.

Proton is targetting enterprise who would love a secure alternative to Google Workspace. A normal consumer don’t need to put all eggs in one basket. I don’t think Proton is forcing you either. I just use their paid email service.