Advanced → GUI Options contains settings of the web interface itself. They apply to all administrators and take effect immediately after Save, without applying.

Options

FieldMeaningDefault
Log out after inactivity (minutes)An administrator who does nothing in the web interface for this time is logged out and has to log in again. 5–1440 minutes.60

The language of the web interface is set by each administrator in their account menu, see Your account. Switch between the light and dark theme with the moon/sun icon in the top bar; the choice is stored in your browser.