I do create AppStream metadata and testing it with your software center via gnome-software --show-metainfo my.xml
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It seems that gnome-software center can not handle screenshots of regular size. The AppStream specs do not name a maximum size of a screenshot. They only recommend a 16:9 ratio.
The first screenshot you see here is OK. It is 960x540.
But the second one is cropped. It is 1280x720.
Any suggestions how to handle that? To me 1280x720 is a regular size.
Is this a restriction of “gnome-software”? I wasn’t able to test that appdata on another software center.