Could you explain your situation a bit better? The one image does not tell the story unless we also know the actual state of those files.

Some of the files in your capture indicate that they are offline (the globe and arrow icon on the bottom left). This would indicate that those files are not locally available - have either file attribute FILE_ATTRIBUTE_RECALL_ON_OPEN or FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS. We are specifically not creating thumbnails for files in that state because it causes them all to be downloaded, which users (rightfully) complained about. We do however, will SHOW thumbnails for files in that state if already made. As in you can make them available (by using whatever process to download and make them local), view thumbnails, then take offline again.

Other files in your capture are indicating that they are shortcuts or aliases (symlink, reparse point, junction point, mount point, hard link, etc). We do attempt to create thumbnails to shortcut targets, but only if those targets are locally-available.

In T97048#1335274, @Harley Acheson (harley) wrote:

Could you explain your situation a bit better? The one image does not tell the story unless we also know the actual state of those files.

Some of the files in your capture indicate that they are offline (the globe and arrow icon on the bottom left). This would indicate that those files are not locally available - have either file attribute FILE_ATTRIBUTE_RECALL_ON_OPEN or FILE_ATTRIBUTE_RECALL_ON_DATA_ACCESS. We are specifically not creating thumbnails for files in that state because it causes them all to be downloaded, which users (rightfully) complained about. We do however, will SHOW thumbnails for files in that state if already made. As in you can make them available (by using whatever process to download and make them local), view thumbnails, then take offline again.

Other files in your capture are indicating that they are shortcuts or aliases (symlink, reparse point, junction point, mount point, hard link, etc). We do attempt to create thumbnails to shortcut targets, but only if those targets are locally-available.

According to Dropbox 9 of those files are locally on the HDD:

these are all .png files but Dropbox does have some file stream alias thing for smart synced files, before on Blender 2.9x it would just fetch and download those files now it just simply doesn't display thumbnails at all

@Casey (BagelCo) - According to Dropbox 9 of those files are locally on the HDD:

That capture is showing 53 files. It shows only 10 of those files as being locally accessible (green arrow ), while the other 43 are not local (grey cloud) and would have to be downloaded before a thumbnail could be made.

before on Blender 2.9x it would just fetch and download those files now it just simply doesn't display thumbnails at all

Yes, this is a change in behavior in response to user complaint. They did not want all their files to be downloaded simply because they browsed there while in thumbnail mode. This could take quite a long time if the files are large and/or the connection is slow.

But you can still get thumbnails yourself. Just make the files local, view in thumbnail mode, then take the files offline again. Afterward we should still show the existing thumbnails even though we won't make new ones while in the offline state.

If I'm not mistaken, not loading the thumbnail of non-local files was an intentional change to avoid problems like T87621: The Blender File Open dialog triggers OneDrive Files On-Demand downloads

I tried implementing a feature that reads thumbnails from Thumbs.db file:
D11100: Windows: request the OS for a thumbnail or icon

This would work around the problem. But the feature was never finalized.

So in my view this is a trade-off between displaying thumbnails and inadvertently loading files from OneDrive.

@Casey (BagelCo), does what I said make sense to you?