Who I have the same questioned this topic

Ever since the system update was done a couple of days ago, my split screen is not working correctly.  I USED to be able to display a split by choosing any 2 windows I had open, as long as they had the double bar icon on the top right of window.  Now, I can only choose one open window for the top view, and it displays apps for me to choose for the bottom.  Not helpful. At. All.

How can I fix this?