Hi Jack,
Thanks for your post. Based on my research, custom themes also could cause this problem, check if you are using a custom theme and enable the default Windows theme to check if this fixes the problem.
1-Click on Start then click on Settings
2-Click on Personalization then click on Themes
3-If you are using a different theme, select the default Windows(check the image below) and check if you are able to change the desktop background.
Also, a possible culprit is the option "Other Windows settings" in the sync settings which may be changing your desktop background with the version saved in the cloud. You can try to disable it and check if fix the problem.
1-Click on Start then click on Settings
2-Click on Accounts then click on Windows backup
3-Switch off the option "Remember my preferences"
4-Then try to change your desktop background again
Here are other troubleshooting that you can try if the problem persists.
Solution 1: Perform a clean boot to check if a third-party app is changing the desktop background. You can see how to perform a clean boot at this link. https://support.microsoft.com/en-us/topic/how-t...
Solution 2: Disable the slide show in the power settings
1-Right-click on Start and click on Run
2-Type: Control Panel and click on OK
3-Click on System and Security then click on Power Options
4-Click on "Change plan settings" then click on "Change advanced power settings"
5-Click to expand the "Desktop Background Settings"
6-Change to Disable or Pause for both options Battery and Plugged in
7-Click on Apply and Ok to save the change
Solution 3: Disable the desktop background change using the Local Group Policy Editor or Registry Editor. You can see how to disable the desktop background change at this link. https://www.makeuseof.com/stop-others-change-wi...
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
Best Regards,
Ian Xue
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