This question is about the meaning of する in phrases like 偉そうにする, 幸せそうにする, and 楽しそうにする
Is this usage used to describe the way they do things/act, as opposed to doing a specific verb such as in the cases of 美味しそうに食べる。So for example, 偉そうにする could describe the way the person talks, walks, their body language etc. The given example of もっと楽しそうにしたらどうなの in full was せっかくの旅行なんだからもっと楽しそうにしたらどうなの which was said to someone who was complaining whilst they had come here to enjoy themselves. Now from context it clearly means something like "how about you/why don't you try to enjoy yourself more(or I'd phrase it "at least try to enjoy yourself"), but I don't quite see grammatically which usage of する this would come under.
Edit: Just adding some of my thoughts. Would it be like 幸せそうにする > act happily > be happy?