I'd like to lock my Debian10/KDE system to one program and prevent any interaction of a user with anything beyond the always-on-top fullscreen program, making it impossible to shut down, to minimize, to open the process manager and to show the tray bar by pressing the Windows key.

In particular I'd like to lock it to the media center Kodi in a way that closing/minimizing it or opening other software requires the root password. Is this possible with some software or CLI commands / parameters within the current session? And if not how could this work (get implemented technically)?