Hello, I have found out recently that arch linux has a package called libappimage which allows you to see the icon of an AppImage file in dolphin (like it does in the file picker). Unfortunately that package does not seem to be in the openSUSE repositories.
I haven’t used libappimage the way you’ve described, in the past I generally used appimagelauncher, but recently discovered the flatpak app GearLever.
Bboth of these tools move the appimage file you have downloaded to a specific folder, and create a .desktop file so that the appimage is integrated in the system and can be launched from your app menu.