Question: If a sin occurs, does its occurrence prove that Allah approves of it?
Answer: No. Will concerns the occurrence of an event; approval concerns whether it is pleasing and acceptable. The occurrence of a sin does not make it lawful or approved.
وَلَا يَكُونُ إِلَّا مَا يُرِيدُ.
Nothing occurs except what He wills.
Follow-up: What, then, must the person do?
Clarification: The revealed command remains the standard. One must avoid forbidden acts and repent after wrongdoing; decree cannot be turned into a legal or moral excuse for disobedience.