I think it wasn’t from the Arian heresy. Arianism consiJesus yo be that Jesus Christ is the Son of God who was begotten by God the Father in time ie that the Son of God did not always exist but was begotten within time by God the Father, therefore Jesus was not co-eternal with God the Father.
Arianism holds that the Son is distinct from the Father (and therefore subordinate to Him).
Islam seems to be from a mix of Gnosticism (they variously believe that Jesus either was replaced on the cross by another man (Simin of Cyrene) or was a phantom. Both are in the Quran;
And Arab converts to Judaism like Dhu Nuwas,Yūsuf Asʾar Yathʾar, a Jewish king of Yemen between 517 and 525–527 C.E., who came to renown on account of his persecutions of peoples of other religions, notably Christians, living in his kingdom.
And Arab paganism with the djinn (according to the Quran Satan is a Djinn not an angel, and djinn are made from fire, Angel’s from air and man from earth)
And Zoroastrianism especially Zurvanism with its stark good and evil contrasts.
To me it seems so likely that the Arab mercenaries fighting for the Sassanid and Byzantine empires in their 80 year war got tired of not getting paid, took over some parts and were astounded by how easy it was as the two empires were exhausted by the century long war and the justinian plague. They were some flavour of Ebionite ie Jewish Christians who then junked all of the Christ is God belief in the 8th century
Good points. You’re right it wasn’t Arianism itself, but Islam grew out of the same context that saw almost all the barbarians outside Roman control embrace unique interpretations of Christianity.
For the Visigoths and Vandals it is labelled as Arianism, for the Syrians Ebionism. For all of them it is a mix of local traditions and Christianity with non-trinitarism as a common denominator.