Thank you for responding, Kevin! I figured it out early:30 this morning. I copied the system info available in Photoshop on both of my computers then compared them. It seems that when I clicked "Application Optimal" in the Intel Graphics and Media Control Panel, Photoshop went into "Scale UI 200%..." mode; and neither reverting back to the default graphics settings, nor uninstalling and re-installing the graphics driver, changed it back. Luckily, the preference option to undo the unwanted change in Photoshop was one of the ones still visible/available in the massively oversized, virtually useless, menus. (I don't know, but maybe Intel will want to leave this thread intact in case someone else has the same problem.)
I'm glad you answered, though, because I now know about the CTRL+ALT+F8 to reset the graphics settings!