This video takes a detailed look at the mixer module in MuseScore 4.
The mixer is a great tool to control how your score sounds and there are many things you can do with it to improve how your score sounds, including choosing the sound library, volume and stereo panning, and adding VST effects.

00:00 Intro
00:17 Opening the mixer
00:26 Changing playback sound library
01:12 Volume and panning
02:03 Mute and Solo
03:09 Adding effects
04:31 View Options
05:27 Playback setup
05:45 Undocking
05:49 Metronome control
06:33 Conclusion