Open file in Finder does not work on App launch

I have a strange issue for my SwiftUI based App on macOS.

Opening and saving a file works well when the app is already open.
But when I double click a file in Finder to launch the App the file is not opened.
When I double click the file again it gets loaded.

I assume that I missed something simple but I can't get a clue from documentation and internet searching.

Any clue how to proceed to open a file on application launch?

To answer my own question:
There is currently no "SwiftUI like“ way to handle this.
So use just the old way via AppDelegate:

final class AppDelegate: NSObject, NSApplicationDelegate {

    func application(_ application: NSApplication, open urls: [URL]) {
        // Read the provided URLs

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