Sound and Volume Mixer

Output and input devices, balance, over-amplification, each app's volume, system sounds

Settings → Sound.

Output: the device (speakers, headphones, HDMI, Bluetooth), volume and left/right balance.
Input: the microphone and its level.
Volume Mixer: every app playing sound right now, with its own volume slider and mute button, updated every two seconds. The same list is under the devices in the Control Center (arrow next to the volume).
Over-amplification: lets the volume go up to 150%, everywhere: here, the Control Center slider, the volume keys and the wheel over the top bar.
System Sounds: the startup and shutdown sounds, on or off, with a preview.

Media keys change the volume with an on-screen indicator. Sound runs on PipeWire; per-app volumes are set with wpctl, which also works from a terminal (wpctl status).