Hi All - Noob here. I recently noticed that the thumbnails don't load for images that are stored in Onedrive as "online only". I came across an old post on this topic that indicated this issue should have been resolved with a previous release, but seems to still be happening.
Is there a setting that maybe I'm missing or is this still an issue?
Can see them in File Explorer? If you can't, it may be because OneDrive doesn't support generating server-side thumbnails for that type of file.
We also have some fixes coming for other OneDrive issues (due to Microsoft essentially sabotaging OneDrive in any process that doesn't run out of the Windows directory). You can try those fixes early by downloading the current beta (12.21.2) and setting this in the registry:
HKEY_CURRENT_USER\Software\GPSoftware\Directory Opus
OneDriveBugMitigation (DWORD) = 0 (zero)
Once 12.22 is released, the registry value will no longer be needed, at least assuming no issues are reported with the betas before then. (So far, reports are that the fix is working well, from people who have tried it.)
Leo - thanks for the quick reply. Yes, I forgot to mention that the thumbnails are working fine in File Explorer. I'll try your suggestions and will let you know how it goes. Thanks!
FYI - this did the trick. 
Thanks!