I'm using Windows. I edited the image, then did a Save As by adding the extension .jpg to the name. because there was no other way to add it in. The Affinity logo appeared on the thumbnail. You are right about the default app settings... it did default to Affinity... but when I used your suggestion to open with something else, I first tried opening with Windows Photo Viewer, but a pop up message told me "Windows Photo Viewer cannot open this picture because either Photo Viewer doesn't support this file format, or you don't have the latest updates to Photo Viewer." (My computer updates regularly). I see the problem... when I try to Save As, it tells me the photo will be an Affinity file, and does not allow me to change the words 'Affinity file' to '.jpg', or to anything else. Finally I went to the space for the file name and added a .jpg extension, but of course the space below it was still telling me it is an Affinity file. A blank thumbnail showed up in that folder, with the new name & .jpg, BUT my image was not on the thumbnail, it was only an indicator that the thumbnail was a Windows Photo Viewer pic (painting of water, mountains, sky with clouds) and it refused to open with Windows Photo Viewer, just gave me the same msg that either Photo Viewer doesn't' support this file format, or I don't have the latest updates to Photo Viewer. HOWEVER, it DID open in Affinity when I asked it to, even with the .jpg format. I cannot upload those Window photo Viewer pics into this space with the uploader, it recorded the name at the uploader, but the msg says Upload Failed. It shouldn't be this difficult. I'm grateful for your suggestion, as it gave me a few other ideas too, but nothing seems to work. I still need assistance... but what?