[MU4 Issue] New Score - Opens complete new instance when score already open

[lengthwave]

Describe the bug
Creating a new score when a score is already open automatically opens a complete new instance of MuseScore.

To Reproduce
Steps to reproduce the behavior:

1. Open a score
2. With score open, select "File > New ..."
3. See described behavior

Expected behavior
Like Logic, Sibelius, or other popular applications that are both resource intensive and use VST, there should be a separate instance opened as a window on top of existing instance, without a redundant icon in the OS dock/systray.

User should be prompted with choice to close existing score or open new instance.
New instance should open, but without redundant icon.
User can toggle between sessions using navigation window (maybe under View?).

Screenshots

Platform information
OS: macOS 12.2, Arch.: x86_64
MuseScore version (64-bit): 4.0.0-2214419458
revision: github-musescore-musescore-df96a36

[lengthwave]

@Tantacrul - FYI

[Tantacrul]

This is actually a MacOS-specific problem (not sure about Linux). On Windows it works as expected. Let me look around and see which solution is most common / works best. Agreed the two tray icons are annoying.

[jeetee]

Can we close this one in favor of #12647 which contains more developer-oriented argumentation around this issue?