When 勉强 means “contrived, unnatural, artificial”, it is similar to 做作. In such circumstances, 勉强 actions as an adjective. When something is said as 勉强, it is so unnatural that it has a false quality and makes people feel embarrassed and disgusted.
Her singing is all right, but her acting is overdone.
He handled that problem in such an unnatural way. No one is gonna get satisfied with it.