Hiding a part and keeping the part playing.

@keithcsmuhutc > I used to be able to hide a part and still hear it playing.

I think you've encountered the fact that many aspects of the MS4's Instrument panel are both ill conceived and poorly executed, for instance:

• I'd like to see show/hide fully decoupled from the Mixer's mute status... or at least allow the user to decouple it.

• The average user would likely assume that double-clicking the Name would open it for editing. But double-clicking the Name duplicates the function of the disclosure triangle ... so then we need the gear, which only affords the option to edit the Name and Abbreviated Name.

There's plenty of discussion in these threads:

    https://musescore.org/en/node/341213#comment-1225057
    https://github.com/musescore/MuseScore/issues/18867
    https://github.com/orgs/musescore/discussions/15945

Now, to your present need ...

Yes, in MS3's mixer you could uncheck Play Part Only. (When checked it essentially soloed the Part.)

It's not nearly that simple in MS4. Though you may get relief by toggling open the Instrument. Once "inside" the Instrument toggling visibility of a Staff does not automatically mute the track in the Mixer.

Alternately, when you have a part open, click a single note as your starting point, and in the Mixer unmute the tracks you want to hear.

Note that making a range selection* automatically mutes all other tracks. But after play has begun, if you find you're not hearing what you want, you can click in the white space to deSolo the Part. Weird, huh? And I don't know if all this is documented.

I'm unclear about the various ways that Mixer tracks get muted without me explicating click the M button; I'm just glad that we can now override the auto-mute behavior in the Mixer.

The Handbook's errors and omissions regarding Range Selection:

• The simplest way to make a range selection is to click in the "white space" in a measure.

• the Handbook fails to describe the appearance of a range selection. MuseScore depicts a range selection by a blue rectangle that surrounds the selected notes.

• the Handbook strongly implies that a range selection must extend "across a given set of staves" but actually MuseScore happily makes range selections = on a single stave.

I'd edit the entry but currently the Handbook is locked pending the new format.

As you say, the only way a part won't be heard is if it is muted in the mixer. let's say I have a string quartet score open. I want to see only the 2nd violin part but hear all the others. Open the Instruments palette. Next to the 1st violin eyeball select the down arrow. Move down to the new entry and click. This turns the entry blue. Now move left to the eyeball and click. This makes the part invisible, but you will still hear it. Repeat for other parts.
I can't tell you if it is better or worse than MU3. I don't use the process. But the above is how to set it up in MU4.

I also don't know if this is in the manual. I'll take a look.