Is it possible to go completely full screen?
I have hidden all of the Toolbars possible, and pressed Ctrl-U to go full screen, but there are still the top menu-bar and the Parts. Is it possible to hide everything and bring them back using a key toggle? 
Comments
Not currently - what you have is the best you can do. Well, there is an unsupported way to lose the menus by checking the menus box when creating a custom workspace, then finding and hand-editing the resulting workspace file to remove the menus. And hoping you remembered first define a shortcut to display the workspaces toolbar when you want to switch back.
In reply to Not currently - what you… by Marc Sabatella
Thanks. And there is no way to hide the Parts right? Now they take up 2 lines. And they can't be moved and merged like other menu items. That's probably sth I want to suggest as a new feature.
In reply to Thanks. And there is no way… by Jubinell
Pretty much everything about how the windows are organized has been or is being redesigned for MuseScore 4, so you might want to check out a nightly build, or wait for the alpha, before thinking through any concrete suggestions.