Jesus is quoting from Psalm 82
PSALM 82:6 I said, “You are gods, And all of you are children of the Most High.
By convention, upper case ‘God’ is a reference to the Almighty God, YHWH. Lower case refers to other god(s).
The differentiations between upper and lower case is at the discretion of the translators. It is meant both as a means of respect and to help understanding. The decision as to which, upper or lower, is made by context.
As for whether plural or singular, this is usually made clear via the Hebrew structure. In verse one of Psalm 82, the word elohim is used twice. One, the first occurrence is clearly singular, the second use is clearly plural.
Lower case ‘gods’ are created entities. So not omniscient, not omnipresent. God ‘created’ the [lower case] gods. They were, in fact, sons of God - angelic beings, angels. As to how they became to be ‘seen’ as gods, we see this in Deuteronomy.
In Deuteronomy, Moses is recounting the history of Israel. And he backgrounds the context of their history by explaining what lead to them being a separate nation, the one chosen by God - for himself. We read ....
DEUT 32:8 When the Most High gave to the nations their inheritance, when he divided mankind, he fixed the borders of the peoples according to the number of the sons of God.
These ‘heads of the nations’, those sons of God, became their, those nations ‘gods’. And, they we’re the ‘gods’ the Israelites were repeatedly warned about, and, commanded not to ‘bow’ to, or come ‘under’.
When the first commandment talks about not having any other gods before Me (God) - theses gods being talked about were literal, ‘real’ gods and not ‘just’ stone images.
This section in Deuteronomy is the incident at Babel. When the people of the [whole] world rejected Him. So he essentially divided them up, and put the sons of God (angels) over them. Then he choose Abraham to be the ‘father’ of his nation, the one set aside for his purposes.
So gods = angelic beings, not ‘gods’ that are equivalent to a God. There is only one true God, Only one who is omnipresent, omniscient, Almighty.