Why do my old layers disappear when I add a new layer?
I am trying to learn Photoshop Elements 2022, using a PC. In this particular case, I am trying to replace the background of a photo with a new background taken from another picture, following this YouTube video:
https://www.youtube.com/watch?v=0kADZHaZmiY
In the process, I have to first open the picture whose background I want to remove, then make duplicate layer to work on, saving the original one as my background; no problem, so far. Both of these layers are visible in the layer panel to the right side of the screen, as they should be.
The second step is to open a second picture which contains the new background (a blue sky, in my case) that I want to place into the first, original picture.
However, whenever I open the second picture containing the sky I want to use (at 2:25 in the video), the first picture disappears from the main work area of Elements as well as from the two above layers in the layer panel. In the video I am following, neither the picture nor the first two layers disappear when he opens the second picture, so I am doing something wrong.
So, my question: Why did my first layers disappear from the work area as well as from the layers panel?
Any help would be greatly appreciated.

