God is the cause of Sin in the sense that He intentionally created beings not only capable of sinning but whom He knew in advance would sin. Therefore God with full knowledge that Lucifer and Adam would sin created them anyway with full capablity to sin. YOU CANNOT DENY THIS if you have anything between your ears that is working.
However, God not only created beings with the capability to sin but created them to be responsible for their choices.
Now, ask yourself why did God go ahead and create beings with that capability and responsibilty that He fully knew in advance would sin and bring chaos into His world?????? This is a question you do not like to consider because it makes your head hurt and if anyone else answers it, that answer gives you fodder to charge them with speaking out of both sides of their mouth and other stupid charges you have made.
The answer is that God PURPOSELY DESIGNED THAT SIN WOULD COME INTO THE WORLD and that is why He went ahead and created such beings knowing fully well they would sin before He created them IN ORDER T

VER RULE sin and use it for the ultimate good of His elect and His own glory.
Now, if you do not think that is the proper answer, you tell us why would a holy God intentionally create beings He knew full well in advance would sin but went ahead and created them anyway??????