Here it is explained in detail how the ic_launcher icons are generated. However, since AI2 does not create a Play Store icon. I still see no need to upload the launcher icon in AI2 with a dimension of 1024px (except for iOS). I could not find any differences in the quality of the icons on different devices (with different densities) if I created the icon (png) with 1024px, 512px or 192px.
If I'll create an iOS app with AI2 (hopefully soon), I would create an extra AIA anyway. Because some assets would then have to be changed. Among other things, e.g. the audio files (ogg formats are not supported by iOS). So for iOS I would then upload a launcher icon with a dimension of 1024px to the assets.
https://romannurik.github.io/AndroidAssetStudio/
See also here: App Inventor version nb181 release scheduled for December 19th