The Thumbnail is not displayed in the cell. Its displayed in the preview of the formula and also in the info but not in the cell itself.
What’s displayed in the thumbnail is obvious really depending on the content, it’s contrast and it’s size displayed.
See screenshot below, where a text document is not really clear and the presentation shows well the picture of a tree in the slide.
For me the cell is completely empty. Tried it with PDF, images etc. For some reason the thumbnail is not displayed
My advise is to contact firstname.lastname@example.org , rather sure that they will be able to see behind the scenes something more.
Success and it would be great if you could share the outcome
Hello! Change format to Image Url)