Hello Reilly. To make slideshow work again, first go to Settings > Personalization > Background and change the background to Slideshow. Then, click Browse, and then choose a permanent folder (e.g., C:\Wallpapers) that contains only image files do not use Downloads, or any folders on external drives. Next, save your current theme with Settings > Personalization > Themes > Save theme, and call it something like “SlideshowFix”. To stop Windows from changing your settings back, go to Settings > Accounts > Windows backup > Remember my preferences, and turn off Other Windows settings. Finally, you need to open Run (Win + R) and type %USERPROFILE%\AppData\Roaming\Microsoft\Windows\Themes. Then Remove any slide show.ini or corrupted theme files left behind. This will clear old slideshow triggers and keep your background setting consistent.
Here's the reference: Win 11 changes slideshow setting to picture
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