Isn’t there a menu item to close the currently open File of Project? How do I make changes permanent? I see “Quit” and then I’m asked to commit changes. It would be more convenient to have an explicit close, then stay in the app and open another project. The way it works at the moment requires to re-open the app.
I wonder how this is not obvious 
There are even three different ways to close or save a project. The Project menu item provides menu entries for closing & saving a project. And both have a keyboard shortcut. And both are also visible as buttons in the UI.
(the tooltip of the ‘X’ button is currently cut off, fixed in the next release)
As you are pointing at it I can see it now. 
I was expecting a Save,Save As menu entry as in so many applications. And Save is actually in the project drop down. I was searching a Save entry in the File-dropdown. Sorry for my blindness.