Cannot delete FortinetClient from Mac Application folder

So you are saying the FortiClientUninstaller.app didn't actually uninstall FortiClient?

FYI, you will still have parts of the FortiClient software in the bowels of macOS since this type of app must install components into the lower layers of macOS. Apps like the FortiClient app must be uninstalled by using the developer's uninstaller app which can sometimes be a menu option within the main app, sometimes it is an option when you run the app's installer again, while other times the developer may provide an uninstaller app with the application in the Applications folder, or it may need to be downloaded separately from the developer's website.

As @Barney-15E mentioned, you should have run the FortiClientUninstaller.app you referenced the command line and deleted from the Applications folder.

Generally an app installed from the Apple App Store or one where you drag the downloaded application into the Applications folder will just require you to move that app to the Trash to uninstall it. However, if you must run an installer app to get the application installed to the Applications folder, then you should be using the app's uninstaller to remove it from the system.

Hope this helps you in the future.

thank you !!! you don't know how much that helped me !