ADDENDUM:
Every folder that I open has the "Create Document" icon in the first position, which I don't recall ever seeing before when browsing files in the app, so I have to assume that its appearance there - and the fact that it's the only file icon that CAN be selected - has to be significant. Also, FWIW, the fact that the + sign on it is in the same orange as all of the top bar items.
If I select that and create a new file, as long as that file is open, I can use the regular File menu to open anything else. And, in fact, once I have ANY file open, I can open anything else, but if I close all files, I get kicked back to this screen, where before I would still be on the standard work area, with the File menu active.
A-a-a-a-a-a-a-and I just realized that I *CAN* open .artstudio files from here, but no other file format. Is it possible that this is actually a normal start screen that, somehow, I bypassed every other single time that I used the program before? Or is it something that normally stays hidden behind the scenes that I somehow got access to and can't put back?
I suppose that, as long as I *NEVER* close all files, I can get ASP to work the way that I'm used to, but it seems a pretty kludgey solution.