(Android app version 1.32.9) The last button (mouse receiver / "Maus-Empfänger") for setting permissions is not clickable with the three legacy "back / home / apps" buttons enabled, because these three buttons are above the button. You can enable the three buttons on android in the settings -> search -> navigation mode ("Navigationsmodus", "Bedienung über 3 Schaltflächen"). Afterwards select a device in the app and scroll down all the way.