Yes, the file you attached does open, it's a white circle on a black background. Here is one the images that won't open.
In Fusion, the file name appears in the Loader but nothing appears in the viewer.
I wonder if the problem is that the IFF file type is associated with Photoshop as its default app. The image will open OK in Photoshop. I can't change the file association as in Windows Settings the only options that appear are Photoshop or Choose an App from the Store. In the 'Choose default application by file type' in Windows Settings, the .iff file appears as 'Adobe Photoshop IFFFileType.19'. When I open the properties of the image and click 'change', Fusion appears in the options but the file association resolutely stays with Photoshop! Where it says 'this file came from another computer and may be blocked' I clicked 'Unblock' but still couldn't change it. I don't know what else to try.