Is the statement of Ibn Abbas (may Allah be pleased with them both) that whoever combines two recitations in one prayer has invalidated his prayer authentic? And is it permissible to combine the recitation of Qalun in the first Rak'ah and the recitation of Warsh in the second Rak'ah?

We have not come across what was attributed to Ibn Abbas, but it is permissible to recite in the first rak'ah with the narration of Qalun and in the second rak'ah with the narration of Warsh. Every narration whose recitation has been authenticated is permissible. Ibn al-Arabi al-Maliki mentioned that a Muslim is not obliged to recite with the recitation of one person, and it is permissible for him to recite Al-Fatihah with different recitations, because all of them are Qur’an.