Top menubar has disappeared across all apps - not just full screen I believe that I typed some keyboard combination in a fullscreen app to hide the top menu bar.  Methinks it were Adobe Reader, but uncertain at this point

Actually even that did not do what was intended:  it just put blank space where the menu bar had been - it did not reclaim that space for anything useful.

Now the menubar is gone for all apps.

Any way to unhide it?
move the mouse pointer as high as possible on the left upper corner os the display screen, this will make the top bar of the application visible, click the round green dot and the application will be smaller, so that you have the top menubar visible again.