Samsung
Change Home Screen Wallpaper auf Samsung
Samsung One UI splits wallpaper settings into two independent slots: one for the home screen and one for the lock screen. Picking a new photo without confirming the target screen is the main reason a change does not appear where you expect it.
To set a photo as the home screen background, go to Settings ➔ Wallpaper ➔ Gallery ➔ Select a Photo. After cropping the image, tap Done and choose Home screen when the system asks where to apply it.
Selecting Home screen and lock screen instead applies the same photo to both, which overwrites any custom lock screen wallpaper you had before. If you only want the home screen updated, always confirm the specific option.
The same menu also lets you switch to preinstalled wallpapers or packs downloaded from the Galaxy Store, using the same target-screen step. If the photo looks stretched or cropped oddly, the issue usually sits in the crop step before Done, not in the wallpaper setting itself.
If the wallpaper reverts after a restart, check whether a theme or icon pack is overriding it, since themes can reset backgrounds independently of this menu.