GNOME sushi not working on desktop in Ubuntu 19.10
GNOME Sushi works fine within Files app. I can preview files with space bar within any folders of the Files app. However, pressing space bar has no effect for the files on desktop. Do I miss something?
No, you do not miss anything.
In Ubuntu 19.10, icons on the desktop are not anymore provided by the file manager Files (a.k.a. nautilus), but by a separate Gnome Shell extension, "Desktop Icons". Sushi works with Files, but not with the extension.
To preview files that live on the desktop, you can go to the Desktop folder in Files.