Don’t forget the Plague of Justinian & the Volcanic Winter of 536 AD both events set the stage for societal collapse particularly in the East.
Possibly, but I'm not sure about those - wasn't Anatolia and Italy more affected than the parts that fell to the Arab empire?
I also think it was the stupid in-fighting caused after Chalcedon AND the persecution of the Jews
when the Arabs took over the Levant, Egypt and North Africa, the Copts, Syriac Christians as well as the Jews helped the Arabs take over - the Arabs were initially "our religion is ours alone, we don't want none of you losers"