On a new installation of the app downloaded from the web, the first launch could be prevented by the operating system's Gatekeeper secure technology.

Gatekeeper is a technology that Apple has implemented in macOS to protect you from downloading and installing malicious software on your Mac. You can learn more about Gatekeeper and other security features visiting this Apple’s Site page or by clicking on the small button with the question mark that appears in the box. This problem does not occur for apps downloaded from the Mac App Store but only for the ones downloaded from the web.

Here is a simple procedure to open the app:

1. Locate the app you want to open (don’t use Launchpad to do this. Launchpad doesn’t allow you to access the shortcut menu).

2. Control-click the app icon, then choose Open from the shortcut menu.

3. On the dialog box, click Open.

Note: now the app is saved as an exception to your security settings, and you can open it in the future by double-clicking it just as you can any registered app.