I have regularly used the image background style of the group component to display PDF thumbnails. I think I got the idea from a video by @gregjohnkeegan
Here is the setting:
And here is the result in Apple Safari:
On Windows computers (Chrome, Edge, Firefox), however, the thumbnail is not displayed and I get the error General warning - The image could not be loaded:
The image displayed is a JPG.
Any ideas why is this so and is there any more general way to display PDF thumbnails?