Is it permissible to prepare and distribute food after the death of the deceased, and to recite Surat Al-Fatihah with the intention of its reward reaching the deceased, and is the grave desolation prayer (Salat Wahshat Al-Qabr) legislated on the first night after burial?

If the intention behind preparing and distributing food to the poor is to seek proximity to Allah and dedicate its reward to the deceased, then there is no harm in it, as long as it is not accompanied by an unlawful act such as a gathering for condolences or a collective recitation of the Qur'an. As for preparing food and gathering people for it, this is considered a form of wailing (niyaha) and innovation (bid'ah) that goes against the guidance of the Prophet, peace and blessings of Allah be upon him. The belief that this act benefits the deceased is incorrect; rather, it harms the deceased. Furthermore, recitation in the manner mentioned in the question is not legislated, nor is the "Salat Wahshat al-Qabr" (prayer for the loneliness of the grave), as neither has a basis in Islamic law and both are rejected innovations.