How do I keep the iPhone 13 screen on in landscape mode for a photo slideshow?

Device: iPhone 13

iOS version: 18.3.2

While I'm working, I want to have my iPhone display the wallpaper shuffle when it's sitting on my desktop, like one of those pictures frames that people have at home, to just display pictures. However, it doesn't stay on for more than 20 seconds, then the screen turns off, and a few seconds later, when, I suppose, it detects that I'm looking at it, it turns the screen on again and shows another picture.

So, the two problems I'm having are:

• How do I force the screen to stay on? I don't like the constant turning off and on
• How to get the iphone to select more pictures? It always displays the same small set of pictures,

[Re-Titled By Moderator]