Windows theme revert back to Dark mode after each restart

Hello Allon,

Thank you for posting question on Microsoft Windows Forum.

Since you have already tried the advanced registry and file permission fixes. When settings revert on restart despite those changes, it highly probably points to one of two things either a sync setting or a third-party program.

The following are a few of suggestions that you can try to see if it works.

1.Check Windows Sync Settings.

• Go to Settings > Accounts.
• Click on Windows backup.
• Look for "Remember my preferences."
• 
• Uncheck the box for "Themes".
• After unchecking it, set your theme to Light mode one more time.
• Restart your computer and see if it sticks.

2.Disable Third-Party Customization Tools.

• Check any apps that might manage your desktop or theme like Stardock Fences, StartAllBack, WindowBlinds, or TranslucentTB or manufacturer software like Dell Optimizer, HP Support Assistant, Lenovo Vantage which sometimes has its own "theme" or "power" settings that can interfere and even "dynamic theme" apps that change the wallpaper based on the time of day.
• Follow below steps to check.
• Press Ctrl + Shift + Esc to open Task Manager.
• Go to the Startup tab (or "Startup Apps" in Windows 11).
• 
• Look for any app related to customization.
• If you find one, right-click and Disable it.
• Set your theme to Light mode and restart.

3.Undo Your "Read-Only" Fix (Temporarily).

• It is possible you made the file read-only before your Light mode setting was properly saved to it.
• Go back to AppData\Local\Microsoft\Windows\Themes.
• Right-click your custom theme file and go to Properties.
• Uncheck the Read-only box and click OK.
• Now, go to Settings > Personalization > Themes and re-select your Light theme (or your custom theme). This ensures Windows can write the new setting to the file.
• Restart your computer.

Hope the above information is helpful! If it is. Free feel to hit "Accepted" for benefitting others in community having the same issue too.

Hello,

Thank you for providing steps:

1. Windows sync setting is already disabled for me.

2. I don't have any third party customization tools. I had Lenovo Vantage which I uninstalled.
3. I unchecked read-only option for Themes folder and my custom created theme file.

I restarted my PC after following all above steps but still same.

Thank you