Hi,
I am looking for a way to turn off the HUD panel, i.e. the control panel that is displayed in the screensaver below. So that the user does not have the possibility to set it at all.
This can be done - basically you want to use your MDM software to prevent the user from setting Registry Keys (on Windows) or Plists (on macOS). See iScreensaver : Managed Installation for details.
Also, be sure you disable the HUD when you build the screensaver, by turning off the Option. See iScreensaver : Branding Control Panels