Secret chats don’t work between the desktop client and the app, so I would suspect that, like the rest of the messages, everything is saved on telegram’s servers in the clear.
In the end, they hold the keys irrespective of how many algorithms they wrap on top.
I do not feel it is any different from Google Chat, Twitter DMs, etc. They do have a lot of censorship resistant and anti-MITM attack features in between, but they hold the keys by default
I use it for convenience and amazing features, not for security!
