How do I get rid of LrC extra window on my 2nd display?

I am using LrC 15.2.1 on a 16" M2 Pro 12/19 Macbook Pro 32gb/1tb, MacOS 15.7.5 and it is connected to a larger external display.  Been like this for the last 3+ years since I bought this computer.  I use LrC everyday and I have it on my big display.  Strangely, today when I use it though it has started doing something I have never seen it do in the 15 years I have been using LrC.  On my big display is the normal LrC window with the grid, but on my laptop display there is the loupe window.  If I explicitly click on the grid icon at the top of the loupe view to try and get rid of the window on the laptop the result is that on the big display it changes to the loupe view (but still the main LrC window) and on the laptop it changes to a grid display.

I can't figure out how this got started.  Did I do something, maybe accidentally typed a shortcut?  How do I get rid of this extra window on the laptop?  I have tried exiting LrC and restarting, but the same thing.  I rebooted, but still the same thing.