How to create an independent non-modal dialog

I'm trying to extend this solution Non modal dialog

from PyQt5 import QtWidgets
dialog = None


class Dialog(QtWidgets.QDialog):
    def __init__(self, *args, **kwargs):
        super(Dialog, self).__init__(*args, **kwargs)
        self.setWindowTitle('A floating dialog')
        self.resize(250,250)


class Window(QtWidgets.QWidget):
    def __init__(self):
        QtWidgets.QWidget.__init__(self)
        button = QtWidgets.QPushButton('Open Dialog', self)
        button.clicked.connect(self.handleOpenDialog)
        self.resize(300, 200)
        self._dialog = None
        global dialog
        dialog = Dialog(self)
        dialog.show()

    def handleOpenDialog(self):
        if self._dialog is None:
            self._dialog = QtWidgets.QDialog(self)
            self._dialog.resize(200, 100)
        self._dialog.exec_()


if __name__ == '__main__':

    import sys
    app = QtWidgets.QApplication(sys.argv)
    win = Window()
    win.show()
    sys.exit(app.exec_())

Apology if title wasn't relevant. I want to have a dialog/window that is independent of all existing window/dialogs, and can be always interacted with, i.e. GUI loop of application window/any dialogs doesn't block this non-model dialog. For simplicity, I have used global variable dialog in above code snippet which will hold the non-modal dialog instance.

When above program is run, the main window appears along-with the non-modal dialog, and both dialogs are user interactive, but when the button is clicked, the GUI loop of self._dialog starts, and user can no longer interact with the floating dialog, and application window. What I want is to be able to interact with dialog but not with Window

I want behavior similar to the example below:

I opened help dialog from main window, then I opened a non-modal dialog which appears on top of the main window, and can not interact with the main window, but still doesn't block help dialog/window and allows user to interact with this non-modal window i.e. the help dialog in the example.

from How to create an independent non-modal dialog