The screenshot referred to in …appdata.xml had the correct ratio of 16x9 and was successfully built into the previous version of the Flatpak. Now the Flatpak fails mentioning the screenshot, so I’ve checked it screenshot using
flatpak run org.freedesktop.appstream-glib validate ...
but this results in
• file-invalid : failed to load
[popout3d/screenshot.png at main · PopoutApps/popout3d · GitHub]
Validation of files failed
It’s not failing to find the file because that would give a “404” error. The relevant line in …appdata.xml was
<image>https://github.com/PopoutApps/popout3d/blob/main/screenshot.png</image>
Copying that line in my browser goes to the image. In case the checking now requires a size statement and perhaps even a 1600x900 image, I’ve also uploaded a new image with that size and changed the statement to
`<image type="source" width="1600" height="900">https://github.com/PopoutApps/popout3d/blob/main/screenshot.png</image>`
that is also rejected. Since the error message just says “validation of files failed” I don’t really know what the problem is.