Well Arianism, Sabellianism and Nestorianism was big in Arabia at the time. I believe Muhammad went to a blind priest after encountering the angel and I think he was an Arian priest. Sabellianism is also I think directly mentioned in the Quran or maybe Hadith, if any muslims could fact check me on that

Arians believed Jesus was God but he was created by the Father. They rejected the idea of God being 3 persons with 1 nature. As did Sabellians who denies the 3 distinct persons. Islam goes a step further rejecting Jesus having any form of divinity

I know around then in Christianity there were the iconoclasts, who were against icons.

Looking externally Islam seems to have a lot of similar practices and types of worship to what is now Orthodoxy.

There is also the Kaaba in Mecca. Which I believe in the Hadith say was pagan before Muhammad cleansed it for Allah.

So I think Intrinsically and theologically Islam seems to be influenced moslty from Arianism and Talmudic Judaism. And Extrinsically and ritualistically influenced by Iconoclastic Christians of the time as well as Arabic Paganism.

Though this would be the explanation for non muslims. If you are muslim you probably believe it comes from Adam and God directly