What event is commemorated by the formal end of U.S. military combat operations in Iraq?

The event that commemorates the formal end of U.S. military combat operations in Iraq is known as Operation New Dawn. This operation marked a significant transition in the U.S. military's role in Iraq, shifting from combat operations to a focus on advising and assisting Iraqi security forces. It officially began on September 1, 2010, and concluded the combat phase of the U.S. mission, symbolizing the end of an era that began with the invasion of Iraq in 2003.

The other operations listed involved different contexts and periods of military engagement. Operation Inherent Resolve focuses on military action against ISIS in Iraq and Syria, Operation Odyssey Dawn was specifically related to the U.S. intervention in Libya, and Operation Freedom's Sentinel is associated with operations in Afghanistan after the drawdown of the U.S. combat mission there. Each of these operations had distinct objectives and timelines that do not relate to the conclusion of combat operations specifically within Iraq, which makes Operation New Dawn the correct answer.