Samsung
Set Up Screen Saver auf Samsung
The screen saver on Samsung devices only activates while the phone is charging and the display enters its regular sleep state. If nothing shows up, the feature is either switched off or set to an option that needs extra content, like photos that have not been selected yet.
You manage this under Settings ➔ Display ➔ Screen saver ➔ Choose an option. One UI offers a color change, a photo frame, a single photo, and a photo table. Each option has its own settings page, so selecting Photo table or Photo frame also requires picking an album or specific images, otherwise the screen stays blank when it should trigger.
Turning the screen saver off entirely is done from the same menu, using the switch at the top of the Screen saver page. This is useful if you charge your phone overnight and prefer a completely dark display instead of moving graphics or photos.
If Always On Display is also active, the two features can overlap visually once charging stops. Checking both settings together avoids a screen that looks different from what you configured.