Scoliosis, lack of sleep, development of myopia ... Something like that. If we are talking about the impact on the psyche, then all this is nonsense. No shooter will make you a killer maniac.
Games are not harmful to the body in any way. Similarly, you can talk about the dangers of books or music. The lifestyle of some players is harmful, who sit in a chair most of the day, eat fast food and do not go outside. Everything should be in moderation.