Why does God use the pronoun us in Genesis 1:26?

2 reasons: 1 I believe in the Trinity, so that is an US. Second, the word in Genesis 1:26 is Elohim instead of Yahweh. Yahweh means God and God ONLY, but Elohim is another Hebrew word that can mean angels, fallen angels, demons, human spirits, and any other resident of the spiritual realm, it includes God but it doesn't mean God only. So the US could mean the Trinity and also the other spiritual beings in heaven that God patterned mankind after. Elohim can mean God or "gods" small g.

Psalm 82
A psalm of Asaph.

1
God presides in the great assembly;
he renders judgment among the “gods”:

2
“How long will you[a] defend the unjust
and show partiality to the wicked?[b]
3
Defend the weak and the fatherless;
uphold the cause of the poor and the oppressed.
4
Rescue the weak and the needy;
deliver them from the hand of the wicked.

5
“The ‘gods’ know nothing, they understand nothing.
They walk about in darkness;
all the foundations of the earth are shaken.

6
“I said, ‘You are “gods”;
you are all sons of the Most High.’
7
But you will die like mere mortals;
you will fall like every other ruler.”

8
Rise up, O God, judge the earth,
for all the nations are your inheritance.

The "gods" were sons of God, the principalities and powers that were supposed to shepherd the nations back to God after the Tower of Babel, but they didn't do what they were supposed to. They wanted worship for themselves. They are the reasons nation became pagan after the Tower of Babel. But then God curses them and says they will fall and even "die like men".

The members of the Divine Council are the powers and principalities that remained faithful to God. These parts of the bible may seem strange to some, but they are important, that they are truth.