So the Hindu belief in Brahman is very similar to the God we believe in. Hence we do not consider Hindus to be atheists as they believe in God. The problem is that they are polytheists because they worship those idols or other gods. They believe they are divine and worthy of being worshipped. This is shirk. And God never authorized those idols to begin with—they don’t have evidence of that.
Sometimes I say: look at the powerful sun isn’t it a manifestation of God’s power? That’s perfectly fine to say and believe. But sometimes I say: the sun is literally a manifestation of God and so it is to be worshipped. That’s shirk.
As for those Muslim philosophers who say humans are a manifestation of God, there are are two types of them:
1- Those who say it symbolically—meaning we human are a manifestation of Allah’s power and wisdom. We reflect his amazing creation. That’s fine.
2- Those who say we are literally a manifestation of God, and technically we are part of God or God himself—this is shirk and most scholars have rejected that.