In relation to the creation of humans, the phrase ‘very good’ (Gen. 1:31) does not necessarily mean ‘being unable to sin’.
When God made the earth, everything was just as he intended it to be. This included making humans with the capacity to be able to make choices, including the choice between obeying or disobeying God (Gen. 2:16-17; Deut. 30:19). Making people this way was part of God’s plan and, by God’s reckoning, it was a ‘very good’ creation.
So, ‘very good’ can mean something like, ‘Exactly as I intended it to be’.
Humans, with the capacity to choose between right and wrong, are ‘very good’. However, if we choose to do the wrong things then we become ‘bad’ — we have sinned (Rom. 3:9-18). Thankfully, if we turn to God for forgiveness then we can become ‘perfect’ (he counts us as perfect — righteous — now (Rom. 4:5), and we will be made immortal in the future when Jesus returns to the earth for the Judgement (Rom. 2:6-7,10,16)).