Image Icon Preview Not Showing. If thumbnail previews are not still not displayed follow the steps below. Changing the icon scale.
For some reason all my local files in the dropbox folders don t show thumbnails on images anymore. But for the online files there are thumbnails. If this box is already unchecked you may have to fix a corrupted thumbnail cache first.
Changing the icon scale.
Regardless of the outcome if this fix was successful or not you can return to the display tab and change the size of the apps back to 100. If needed close and reopen file explorer after making the change. Once the next startup is complete see if the icons are displaying correctly. Uncheck the always show icons never thumbnails box.