The other reply offered a perfectly good set of corrections but I want to add my own clarifications.
One point I wanted to make in my original comment was that monotheism vs polytheism is not a helpful object category when talking about 2000 year old religions as their adherents understood it. This analytic category is a fairly recent invention. You can make this distinction if you want, but it will be of precious little use for actually understanding the people of the past.
It’s also not helpful to back-project contemporary understandings of Judaism back into the religious context of the 1st century. The idea that the messiah would be in some sense divine, or even that he would be YHWH Himself, is not purely an invention of the Christians, but was present in Jewish groups prior to Jesus. I would argue this has not even been entirely purged from all strands of modern Orthodox Judaism. This doesn’t even get into stuff like the Zohar/Jewish mysticism where you have 12+ special flavors of God.
All of these groups would have insisted that there’s one true God, but they would also have insisted that he had more than one hypostasis.” Romans at the time also believed that a single God could have different hypostases.* Nevertheless despite this agreement they accused the Christians not of being monotheists but of being atheists because the Christians alone refused to pay respect to any of the hypostases of any of the recognized gods.
The idea that Jesus is depicted as having some kind of separate agenda from His Father is also a very bizarre reading of the New Testament. Jesus’ relationship with The Father seems to be much more complex than that since he says The Son can do nothing Himself and that He only does what the Father is doing, that He and the Father are one, etc.
There nonetheless seems to be some kind of distinction between Them, hence the two thousand years of theological debate. If you want some sources on this type of thought prior to and parallel to Christianity, you can read the book Two Powers in Heaven.