How do I use the ico file export?

[manngo]

I have a png image which successfully exports to macOS icns format. However I don’t understand how the ico file export is supposed to work.

All I get is a is a very small file, which doesn’t appear to qualify as a suitable file when I try to use it. (I am using it as an application icon in an Electron application).

If I export using Graphic Converter, it all works as expected.

I have used an original png image 964 × 1148 and another 262 × 304.