Windows Explorer doesn't show video thumbnails anymore [Win11Pro]

I have the same issue, and it is related to video files with sizes larger than ca. 250 MB stored in my OneDrive.

in my personal OneDrive on my laptop, thumbnails for most video files (mp4, mov) are not displayed. It appears that video files starting at around 250 MB are affected. Smaller video files (smaller than 250 MB) do seem to generate thumbnails. Thumbnails for images (e.g., jpg) are displayed correctly (but the file size ist mostly smaller than 250 MB).

The problem only occurs with video files stored in OneDrive. As soon as a video file is stored outside of OneDrive on the local drive, thumbnails are generated. This issue only appears on my new laptop, my old laptop does not has this issue, all thumbnails for video files are diplayed correctly in OneDrive.

My system:

- Intel Core Ultra 9 275HX, Windows 11 Pro, version 25H2, all Windows Updates installed Installed

- OneDrive versions: Build 26.007.0112.0002 (64-bit). After updating: Build 26.012.0119.0002 (64-bit)

All files are fully downloaded locally (Files On-Demand is not enabled).

I executed a couple of troubleshooting steps (multiple times) which were recommended:

- File Explorer => Folder Options:  The checkbox “Always show icons, never thumbnails” is not selected.

- View switched to Large icons / Extra large icons.

Disk Cleanup / Thumbnail cache:

- Cleared the thumbnail cache multiple times using Disk Cleanup, and restarted the laptop.

- Alternatively cleared via Command Prompt (Administrator) by deleting thumbcache

 OneDrive settings and reset actions:

- In File Explorer =>  right-click on OneDrive => Always keep on this device is enabled. All files are locally available (green circle with white checkmark).

- OneDrive => Settings => Sync and backup =>  Download all files selected.

- OneDrive => Settings => Account => Unlink this PC, then uninstalled the OneDrive app, deleted all locally stored files in the original OneDrive path, reinstalled OneDrive, set it up again, and allowed all data to be downloaded locally (green circle). Laptop restarted.

As soon as the locally stored video files are not inside a OneDrive folder - or after Unlink this PC when the files are no longer associated with OneDrive - thumbnails are displayed. The issue only reproduces when the videos are inside OneDrive and fully available offline.

Any ideas how I can resolved this thumbnail issue?

Since video thumbnails depend on codecs:

• Update your video codecs (e.g., K-Lite Codec Pack).
• Or, temporarily uninstall third-party codecs if installed.
• Restart and see if thumbnails return.