Not all dockable panels are saved in Workspace
Create new workspace
Select all options to save settings (Toolbars, GUI Preferences, Menu Bar, GUI Components)
Activate Mixer and Play panel, display them as tabbed See attached screenshot.
When exiting MuseScore and restart MuseScore again to check if all settings are saved.
All settings are saved Except the panels, only usage of Mixer is saved, the play panel is gone
I expect both panels to appear again and docked as tabbed panes as I set it.