There are a few possible reasons why your DNG files are not displaying thumbnails in Windows 10. Here are some suggestions to try and fix this issue:
1. Install Adobe DNG Codec: By default, Windows does not have built-in support for DNG files. You can download and install the Adobe DNG Codec, which enables Windows to generate thumbnails for DNG files. You can find the codec on the Adobe website.
2. Enable thumbnail preview in File Explorer: Make sure that the thumbnail preview setting is enabled in File Explorer. To do this, open any folder, click on the "View" tab at the top, and make sure that the "Preview pane" and "Thumbnails" options are selected.
3. Clear thumbnail cache: In some cases, the thumbnail cache can become corrupted, leading to thumbnail display issues. To fix this, you can try clearing the thumbnail cache. Open File Explorer, click on the "View" tab, and then click on the "Options" button. In the Folder Options window, go to the "View" tab and click on the "Reset Folders" button under the "Folder views" section. This will clear the thumbnail cache and reset folder settings.
4. Rebuild thumbnail cache: If clearing the thumbnail cache doesn't work, you can try rebuilding the thumbnail cache entirely. Open File Explorer, click on the "View" tab, and then click on the "Options" button. In the Folder Options window, go to the "View" tab and check the "Always show icons, never thumbnails" option. Click "Apply" and then uncheck the same option again. This will force Windows to rebuild the thumbnail cache.
5. Update graphics drivers: Outdated or incompatible graphics drivers can sometimes cause issues with thumbnail display. Update your graphics drivers to the latest version available from the manufacturer's website.
If none of these suggestions resolve the issue, it may be worth considering using third-party software that specializes in generating thumbnails for various file types, including DNG files.