Windows shows the wrong icon: file, shortcut or app?
Replacing a file in Downloads does not necessarily change an existing shortcut or a running app. Establish which resource is actually used before rebuilding the ICO or attempting system-wide cache changes.
Keep the icon at a stable location
Move the finished ICO into a permanent folder. For a normal Windows shortcut, open its properties and use Change Icon where available, then browse to that file. Moving or deleting the ICO later can break the reference. A desktop shortcut change does not rewrite the application executable.
Distinguish the surfaces you are testing
Compare the shortcut, the running application and the pinned taskbar item separately. They may obtain icons from different resources. If you own the app, update its framework or package icon configuration and rebuild it; changing a shortcut is not an app packaging workflow. Avoid editing another vendor’s executable just to replace its icon.
Use a controlled comparison
Create a fresh test shortcut pointing to the same target and icon. If only the old shortcut is wrong, investigate that reference or its cached presentation. If both fail, inspect the ICO’s sizes and supported encoding first. Record the application and Windows version when reporting the issue; one converter preview cannot reproduce every shell context.