Theme (light, dark or system)
In Settings → Appearance you choose between light, dark or following the system. On desktop, the theme switch also lives in the user menu (avatar in the top-right corner). On mobile, the switch sits right at the top of the Preferences section of the More tab — no separate screen needed.
Language, time zone, country and units
In Settings → Language you set the app language, time zone, country and the measurement units used in clinical records.