Why do you need a database over a serialized object like a hashmap file if there is only one user and one device?

I guess the point is that you can get away with such sloppy code as long as it is a solo project of a relatively small size.

I am not sure at which point it becomes too big and new features and bugs are just impossible to handle.

It might have been the right choice for Telegram though. Their app feels snappy, so the 'only' big downside is that now it looks like they are going to have to thrown away this entire code base and replace it with the one from Telegram X (a third party client they bought)

I'd be more concerned about the developer side, particularly new developers and OSS contributors, the wide attack surface introduced by such complexity, long-term inflexibility, impossible to track down bugs, etc more than anything. I'm sure they have plenty of people to QA from the user perspective, just clearly not the code.

Maybe the developer was pressured to focus on releasing quickly over code quality...yada yada. The typical startup developer story. But not a story that I like to find in my security-focused software.