Build a simple prop OS on Unity

I own an Escape Room company. For one of our game we need a very simple OS and I can't find even in Kiosk mode something that fits our needs. We use Ubuntu now but we have some issues with file permissions or so. Then what we need : - A "game" that will be in full screen and simulate a real OS (custom with our logo and things like that) - Something I can open in Unity on my own and adapt or make small changes if needed - A login screen with a simple string password field - That brings to a Desktop where there are a few "files" (images and video) that people can "open" (one click to open, then the cross to close it) - People will find USB sticks and SD Card during the game, when they plug one in, it will give them access to files. Maybe USB Sticks can only contains "identifiers" that will make the "game" identify which USB or SD card it is, then give access to those files that are included in the "game" assets. I don't know if I'm clear enough, what I need seems pretty simple, but I'm able to discuss it if needed.