You can set DO to replace File Explorer, but if TB still uses File Explorer, I recommend you enable the Ribbon in FE (Ctrl+F1) and adjust the selections on the View tab to show icons (thumbnails), Preview pane etc.

DO has been always set to replace all file actions as shown in the attached screen shot, and as you can see in the screen shot I sent with the original post FE has already been set to show icons and the viewer pane, it just however shows a stock windows logo for images rather than the real thumbnail or image.

Again may I ask: "is there a way to change thunderbirds default file manager" since it is clearly not using DO and FE most likely has limited functionality because the default handler for pdf files and images is not a microsoft product because DO handles those not FE. Because i do not use microsoft product as default apps for viewing pdf and images I really think it is going to be a hassle getting FE to view those files and preview those images. That is why I think pointing Thunderbird to DO may the the simpler option.

Thank you so much for helping out. Really appreciate it.

I don't use MS apps as defaults for images or pdf files, but thumbnails appear in FE. Having DO handling images, instead of separate apps, may explain why you don't see thumbnails.

I don't know of a way to change TB's default file manager. i assume it uses the system default.