For iOS, there should be a 1024x1024 PNG called iTunesArtwork in the application bundle, for Google Play Store a similar file in 512x512 is required. Is there a way to specify this in the Editor? Or does Unity rely on the icons being uploaded manually to the respective stores?
On Unity we use an icon that is 1024X1024 and it looks just fine on all Android and Apple devices.
In Unity 2019.1 I found it
in iOS Player Settings > Icon > Marketing Icons > App Store Icon
I haven’t found the spot for the 512x512 Android icon, but I haven’t built for or submitted to the Google Play store yet, so I’m not sure what the current requirements are.