Follow step 1 in the instructions above to open Personalize settings.If the above solution does not work to fix your dark mode related issue, ensure that you have turned on the dark mode option in Windows 10.
The file explorer with dark mode turned on should look like this: Optionally, you can switch back to the custom theme you were using if you don’t like the default Windows theme. The dark mode issue should be fixed now.Under Apply a theme, select the Windows default theme.Alternatively, you can access Personalize from the Settings app. Right-click anywhere on your desktop and select Personalize.This workaround should fix the dark mode not working issue. The first solution you should try is to switch your Windows 10 theme to the default theme, then optionally, switch back to your custom theme. In most cases, there will be some bugs or conflicts between the dark mode and the custom theme you are currently using. “Choose your default app mode” missing or not working.
