80x80 icon file is for app testing, and 400x400 icon file is for LG Content Store. However, both files are required for app submission. (See App Resources and appinfo.json.) Thank you.
The largeIcon property is optional. No need to worry about the panel size, etc. As mentioned in the icon property, 80x80 and 400x400 icon files are mandatory and will be resized automatically before use. Thank you.
So then the 400x400 icon file is used for the 126x126 Home Screen panel app icon you mention? How else could a 126x126 icon be filled with a 80x80 image?
As mentioned above, 80x80 icon file is for app testing, and 400x400 icon file is for LG Content Store. 400x400 icon file will be resized automatically before use. Thank you.