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. (This would also require the root-password for the shutdown button within Kodi or at least e.g. a custom key-combination).
Is this possible with some software or CLI commands / parameters within the current session (maybe using KDE Plasma Activities)? And if not how could this get implemented technically?