On views of God presented in the Old Testament (‘YHWH-alone’, ‘YHWH-and-other-gods’, ‘pantheon of gods’, etc.), personally I think there are diverse opinions among the Israelites themselves. My recent Bible reading came up with an example.
“Will you not possess what Chemosh your god gives you to possess? And all that the YHWH our God has dispossessed before us, we will possess.” (Jdg 11.24)
It was Jephthah (a judge of Israel) who said this, and I take this as Jephthah thought (or believe that) the Israelites had a god whose name was YHWH while the Ammonites had a god whose name was Chemosh. Jephthah was a henotheist, so to speak. He worshipped one god, but he didn’t deny the reality and existence of other gods.
It was quite different with, say, views presented in Isa 45.21-22, “And there is no other god besides me… there is none besides me… for I am God, and there is no other”, which was strictly monotheistic, so to speak.
However, perhaps it was safe to say that after the exile (and then to the Second Temple Judaism era) these diversities converged into a single strand, i.e., genuine monotheism, which was of course later on mutated by the early Christians by including Jesus (and the Spirit) into the mix. (cf. Isa 45.21-22 & 1 Cor 8.4-6)