If the brightness slider is missing in Windows 11, first identify the screen you want to adjust. On a desktop using an external monitor, its absence can be expected: use the monitor’s own brightness controls. A laptop’s built-in screen losing a previously available control needs a different check. Open Settings → System → Display and…
Windows says No audio output device is installed, or your speakers have vanished from the output list. Open Settings → System → Sound and check Output first. A missing playback device needs a different approach from a visible device that is silent. If the intended device is absent, check its connection and Device Manager, then…
The Bluetooth switch has disappeared, so there is nothing to turn on. First open Settings → Bluetooth & devices and check whether the switch is missing there too. A button that is off, a missing Quick Settings tile, and an adapter Windows cannot detect need different checks. If Bluetooth is absent in Settings, check Airplane…