[telamir]

it may be a hidden folder idk I found it easy when I went looking but you cant search it just brings up webpage not found you have to click on C: then Windows and scroll down to web there are 3 folders in mine 4K, Screen, and Wallpaper

in the file explorer there is a check box in the view tab called hidden items just make sure there is a check in there then go to the directory

I was looking at the options for the lock screen and there is no random option that I saw ..in theory it shouldn't just choose a random pic it should just stay with what ever its assigned ..there is a slideshow option though