How to change wallpaper of App Screen on iPhone
I don't want to change my lock screen - I want to change the home screen (where apps are) that has turned black!
[Re-Titled by Moderator]
iPhone 12, iOS 18
The pic below may help you.
In the first screenshot, there's no lock icon at the top and it says 'Swipe up to open' at the bottom. That means your iPhone is unlocked but not open.
If you swipe up and open it will not work. If the Screen is locked it will not work.
To change and customize your iPhone wallpaper, you'll need to unlock your phone first. If pressing firmly on the Lock Screen doesn't work, it's because your iPhone is still locked. Don't swipe up to unlock it entirely. Instead, just use Face ID to unlock it normally, and then you'll be able to access the wallpaper options by pressing firmly again.