An a hour ago I used to be able to left button click a track segment and it would highlight it. Now it doesn’t. Also, I used to be able to place a layer on top by clicking to the left of the layer’s colored box under Layer Manager in the upper right. Now neither happens. Also, the current layer used to be dominant in the main window and it would hide the other layers below it. Now it always looks the same with layers being partially transparent. I am bound to have gotten this thing into a mode and I don’t know how to get it back again. Could someone give me a clue to what is going on here?
Do you have accidentally actived the dim mode?
And for track-selection: do you have changed the selection-filter? (bottom right)
Probably accidentally clicked the “All Items” in the “Selection Filter”.
Been there, done that.
I discovered that you can have a pretty marked change of behavior when you change “Tool Sets” by pressing F9, F11 or F12.
Which means you have an ancient pre-historical version of KiCad. I bet you found a 5¼-inch floppy disk from a museum to install KiCad. Can’t you update to v7 which is actually supported and for which you can get help here?