please respect aspect ratio of images. e.g application addons and plasma addons show picture previews instead of an icon but this images are always rectangular what didn't look professional.
Created attachment 106075 [details] wrong aspect ratio as you can see the image is visible in the full preview but didn't work in the app list view and also it didn't work in the preview list abouve description.
Created attachment 106076 [details] frame around picture as icon view it would look very good if you style the apps like babe (kde music player) do.
a lot of online apps crop pictures, so maybe you can crop the image that it will fit the aspect ratio you need.
This was fixed in Kirigami 77c2f3301df1b21d7bcee884fe02d1edc54b12b2