Why don’t I see Wallper in System Settings → Wallpaper?
It appears after you enable it and set a wallpaper. Guide: https://www.wallper.app/support/lockscreen
The Wallper section in System Settings → Wallpaper only appears after the feature is triggered.
Enable “Use Lock Screen & Screensaver” in settings, then set a wallpaper again. This will make the Wallper section show up automatically.
Guide: https://www.wallper.app/support/lockscreen