If you're running dslrBooth in full screen, you can add a PIN under Settings, Show Lock Screen, Security Pin to stop guests from exiting the application.
If your tablet has a touch screen, you'll need to disable three-finger touch gestures in Windows 10/11. Starting from v7.47, dslrBooth will disable the Windows key when the app is running in full-screen.
You might also want to disable the Settings button on the virtual Windows keyboard.