Is it true what is said in some books that Al-Fatiha and Al-Mu'awwidhat are not part of the Holy Qur'an, as transmitted from Ibn Abbas (may Allah be pleased with them both)?

The questioner did not mention the books that contain the statement, but it has been authenticated on the authority of Ibn 'Abbas (may Allah be pleased with them both) that he narrated these surahs as being part of the Qur'an, and this is through the continuous chains of transmission of the reciters, as the recitations of Ibn Kathir and Nafi' were narrated with chains of transmission back to him.