There can be two major causes. The first is when the executable file SettingSyncHost.exe is unable to sync your theme across the machine. The second is when there is a problem with the active theme.

How to create and use the same Office themes across files in Microsoft 365 Your email has been sent Themes were added to Microsoft Office a long time ago, but they’re underused, in my opinion. By ...

While changing a theme on Windows, if you see an error message This theme can’t be applied to the desktop, then this post may help you. This error prevents users ...