If Backdrop wallpapers still appear in macOS System Settings after uninstalling Backdrop, they are usually entries that were registered with macOS for Lock Screen support.
These entries can remain visible under System Settings → Wallpaper even after the Backdrop app has been moved to the Trash. They may appear under a "Backdrop" category, and selecting them may not apply a wallpaper.
If Backdrop is still installed
The cleanest way to remove these entries is to disable Lock Screen support before uninstalling:
- Open Backdrop
- Open Settings
- Turn off Lock Screen Support
- Quit Backdrop
Open System Settings → Wallpaper and check whether the Backdrop category has been removed.
If Backdrop has already been removed
If you no longer have Backdrop installed, remove the wallpaper cache entry that macOS uses for these Lock Screen wallpapers:
- Open Finder
- Choose Go → Go to Folder from the menu bar
- Enter this path:
~/Library/Application Support/com.apple.wallpaper/Store/aerials/manifest- Move
entries.jsonto the Trash - Restart your Mac
After the restart, macOS will rebuild the wallpaper manifest and the leftover Backdrop entries should no longer appear in System Settings.
Why this happens
Backdrop uses macOS wallpaper services to make wallpapers available on the Lock Screen. When an app is removed by dragging it to the Trash, macOS does not give the app a chance to run cleanup steps. This can leave the Lock Screen wallpaper entries behind until the related macOS wallpaper manifest is cleared.