The answer should be obvious, God is good and cannot create what is bad.
The Bible makes it clear that when God made the word, one consistent thing is brought up every time he created something, He saw it was good: https://www.biblegateway.com/passage/?search=Genesis+1
What ever God touches is uncorrupt and pure. There is no darkness in him.
"Habukkuk 1:13 Your eyes are too pure to look on evil;
you cannot tolerate wrongdoing.
Why then do you tolerate the treacherous?
Why are you silent while the wicked
swallow up those more righteous than themselves?"
This doesn't strike me as a God who himself would create evil, in fact it even states the exact opposite. If he was a God who created evil, Why on earth would he then turn around and condemn the evil itself. It's foolish to conceive such a thing.
Here are a few more texts:
"Psalm 136:1 Give thanks to the Lord, for he is good.
His love endures forever.
2 Give thanks to the God of gods.
His love endures forever.
3 Give thanks to the Lord of lords:
His love endures forever."
"Psalm 100:1 Shout for joy to the Lord, all the earth.
2 Worship the Lord with gladness;
come before him with joyful songs.
3 Know that the Lord is God.
It is he who made us, and we are his[a];
we are his people, the sheep of his pasture.
4 Enter his gates with thanksgiving
and his courts with praise;
give thanks to him and praise his name.
5 For the Lord is good and his love endures forever;
his faithfulness continues through all generations."
Read also the whole of Psalm 107, specifically verse 1:
"1 Give thanks to the Lord, for he is good;
his love endures forever."
"Psalm 34:8 Taste and see that the Lord is good;
blessed is the one who takes refuge in him."
Countless texts show that God himself is good, holy and righteous, and I don't really see how much clearer it is than that.
(Take a note Guard of Gold, the Bible demonstrates that God is good.)
Going back to Genesis, What do we have, We obviously know that Adam and Eve were given free will, God wanted to give them to opportunity to follow him, but instead, they chose wrongly when Satan tempted them in the Garden of Eden. As a result of listening to the serpent, Adam and Eve damned themselves and thus fell into original sin. God was aware that Adam and Eve would make the wrong choice, If he wanted to, he could force Adam and Eve to love him, but he didn't. Does Adam and Eve turning evil mean that God himself created them as evil? No. Does Adam and Eve turning evil mean that God himself didn't know the future? No. He knows the future, Open Theism is false teaching.
Plus, the concept of dualism is nothing more than Gnosticism. The Bible as a whole rejects the idea of a second God, including the concept of having Satan as a second God, even 2 Corinthians 4:4 if others wish to use that verse to prove their point, doesn't prove such.
Satan as I have already stated in other papers is NOT omnipresent, he is a creature and by comparison to YHWH, is severely WEAKER than YHWH. Not to mention, the Shema itself testifies "Hear O Israel, The LORD our God, The LORD is one", which makes it very clear that there is only one God who exists, Not to mention, Jesus, himself stated "No one is good EXCEPT God alone". As Jesus is the second person of the Trinity, That by definition makes Jesus YHWH and makes him good, something no one can claim.
God is good, it's simple and easy to prove, it is not a vacuous statement.