I’ve posted about it elsewhere, but for me it has always been more productive to have that kind of stripped down UI, like Composition Mode gives you, but with the seamless option for more. Bear in mind the Scrivener project window can be reduced down to this:

Couple that with a saved Layout that is set to be your full screen default,[1] and now you’ve got “composition mode” that is ultimately capable of doing everything a project window can do, in bits and pieces, precisely for only what you need of it. Maybe focusing on a big freeform corkboard can be just as important and productive for what you’re doing right now, as filling up a column of text. One can have just as much focus when editing, if that is what they want.
I haven’t tested it, but I think that would also trigger when splitting the screen between software. ↩︎