Hi,
Unfortunately, Microsoft Photos does not have a built-in option to adjust slideshow speed. You can work around this by using another slideshow app, creating a video slideshow with Clipchamp, or restoring the old Windows Photo Viewer through the registry. Please note that modifying the Windows registry can be complicated and may unintentionally affect other settings or applications. If you choose to restore the old Windows Photo Viewer, I strongly recommend backing up the registry before making any changes.
If you need additional help, please let me know.
Stay Safe!
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