Hello there,
If you have a preview or thumbnail view set for your OneDrive folder, you should see thumbnails for all files.
If you are not seeing thumbnails, check these features:
If you're using a web browser, ensure the OneDrive.com file viewer is set to Tiles. Learn how.
If you're using a PC/Mac, ensure your computer's File Explorer/Finder view is set to medium-sized icons (or larger).
If File Explorer/Finder thumbnails still don't show, enable "Always keep on this device" for the file.
Hope this resolves your Query !!
--If the reply is helpful, please Upvote and Accept it as an answer–