Can You Find The Mistake?

This picture shows a list of equations that "prove" 1 = 2. Can you find the flaw?

Step 4 isn't dividing by 0. (a+b)(a-b) = a squared - b squared.

b(a-b) = ab - b squared.

Step 5 because you can't divide by a-b, because a-b = 0 and you can't divide by 0.

Nice job AmazingAryan