After Moses died, why were Satan and the Archangel Michael contesting over his body?
You’re referring to the verse in Jude 9. But even the archangel Michael, when he was disputing with the devil about the body of Moses, did not dare to bring a slanderous accusation against him, but said, “The Lord rebuke you!”
The popular answer to this question is that God needed the body of Moses in order to send him back as one of the two witnesses of Revelation 11. In Matt 17:3 on the Mount of Transfiguration, we’re shown Moses and Elijah in physical bodies, recognizable to Peter, so maybe that’s the case. And though Scriptures teach that God buried Moses (Deut. 34:5) no one has ever found his grave. Elijah, of course, was taken live into heaven with his body intact. (2 Kings 2:11)