According to 2 Thessalonians 2:3, that day will not come until the rebellion occurs and who is revealed?

Answer: The man of lawlessness

Paul says the rebellion must come and the man of lawlessness (KJV: man of sin), the son of destruction, be revealed first.

“Let no one deceive you in any way, for it will not come until the rebellion occurs and the man of lawlessness—the son of destruction—is revealed.”— 2 Thessalonians 2:3 (BSB)