Which texts/works were lost due to the Mongol invasions of Baghdad? Baghdad was a center for learning and there seems to be an immense literature loss during the sack of that city, just like the losses from Alexandria library.
There were different phases. In the beginning they just interpreted Quran. Then they started translating foreign works. Later they started doing their own research in chemistry, algebra, medicine, and other disciplines.
From Britannica I read:
In that same capital city was founded the great library Bayt al-Ḥikmah (“House of Wisdom”), which, until the sack of the city by the Mongols in 1258, served as a huge repository for the series of works from the Hellenistic tradition that were translated into Arabic. Al-Andalus became to the rest of Europe a model of a society in which the religions and cultures of Islam, Christianity, and Judaism could work together and create a system of scholarship and teaching that could transmit the heritage of older civilizations and the rich cultural admixture of Andalusian society. Western science, mathematics, philosophy, music, and literature were all beneficiaries of this fascinating era, of whose final stages the fabulous Alhambra palace complex in Granada, Spain, remains the most visible token.
There also were mathematical texts:
The subsequent acquisition of Greek material was greatly advanced when the caliph al-Maʾmūn constructed a translation and research centre, the House of Wisdom, in Baghdad during his reign (813–833). Most of the translations were done from Greek and Syriac by Christian scholars, but the impetus and support for this activity came from Muslim patrons. These included not only the caliph but also wealthy individuals such as the three brothers known as the Banū Mūsā, whose treatises on geometry and mechanics formed an important part of the works studied in the Islamic world.
Of Euclid’s works the Elements, the Data, the Optics, the Phaenomena, and On Divisions were translated. Of Archimedes’ works only two—Sphere and Cylinder and Measurement of the Circle—are known to have been translated, but these were sufficient to stimulate independent researches from the 9th to the 15th century. On the other hand, virtually all of Apollonius’s works were translated, and of Diophantus and Menelaus one book each, the Arithmetica and the Sphaerica, respectively, were translated into Arabic. Finally, the translation of Ptolemy’s Almagest furnished important astronomical material.
Of the minor writings, Diocles’ treatise on mirrors, Theodosius’s Spherics, Pappus’s work on mechanics, Ptolemy’s Planisphaerium, and Hypsicles’ treatises on regular polyhedra (the so-called Books XIV and XV of Euclid’s Elements) were among those translated.