When changing the icon of a built standalone or client-server app in 4D, here are the steps to follow:

1. Use a valid .ico file. One way to assure the .ico is valid is using the site below to convert a PNG to ICO file with sizes 16x16, 24x24, 32x32, 48x48, and 64x64 selected to generate a multi-resolution icon.
https://www.aconvert.com/icon/png-to-ico/

2. Rename the ICO file to the same name as the structure file and place the file on the same directory level. For example, if the structure is named "test.4DB", the icon file will be renamed to "test.ico".

3. Build the 4D app

4. If Windows Explorer still shows the default Volume Desktop icon, Windows Explorer may need to be restarted as the Volume Desktop icon may have been cached. To manually restart Windows Explorer, it can be done either by using Task Manager > right click "Windows Explorer" process > Restart, relogging in, or restarting.