What is the ruling on congregational supplication in a collective form before the opening takbir (Allahu Akbar) between the iqamah and the opening takbir, and what is the ruling on the congregants saying "Ameen" behind the imam in this situation?

The supplication between the adhan and the iqamah has no prescribed textual basis. Persistently performing it collectively is an innovation (bid'ah) and was not done by the Prophet, peace and blessings be upon him, who said: "Whoever performs a deed that is not in accordance with our matter will have it rejected." The Imam must abandon this innovation.