On a new computer running Windows 10 Home, I've installed an image viewing program (ImageGlass) that I've used happily on other W10 computers. But it's behaving weirdly. It is installed and it does function: if I open it and drag jpeg files into it, they open. But if I go to "Set defaults by app" it doesn't appear; and on the regular Default Apps settings page, it appears as an option for Photo Viewer, but the square next to ImageGlass's name is grey with a + sign; the usual blue logo of the program is in other words not shown. And if I go ahead and try to set it as the default program to open photos anyway, it will allow me to do this... but if I then go and try to open a photo, it doesn't work - I get an error message saying, "This file does not have an app associated with it" etc. So basically ImageGlass is there and working, but the Windows 10 settings page that sets Default Apps somehow sees only its name but doesn't connect with the associated program.
Ideas? This is a brand new computer right out of the box. If you need further information, let me know. Thank you in advance.