There's a saying, 'fighters are never the same after a knockout', and this is true in a lot of cases. A high profile example: the former UFC middleweight champ, Usman, was winning a fight easily until in the last minute his opponent, Edwards, kicked him in the head and knocked him out.
In their rematch, Usman was not nearly as good as he was last time. Every time Edwards even feinted a kick, Usman would visibly flinch.
Very apparent that the KO affected him very deeply on a mental level. Usman went on to lose the fight terribly. The fight prior to this, people were having genuine conversations about him being the best fighter alive.
But this is an extreme example. Many people suffer KOs and bounce back, but what I'm saying is that people can get really traumatised by fights yeah. That's why sports psychologists are important.
But I'm talking about real martial arts. IDubbz and Co. were putting on exhibition bouts. The point is that it was for charity, and that it was meant to be enjoyable. No one was getting bodybagged, these people wilfully signed up for it as a presumably enjoyable thing for themselves and viewers.
Exhibition bouts, celebrity boxing, these are not traumatising events. From reading interviews with people after exhibition bouts (usually old boxers in retirement) they always talk about it being enjoyable, cathartic. The trauma from fights is oftentimes as much to do with how it impacts a fighters career. In celeb boxing if you lose you don't worry that you don't get a title shot, or that you won't be able to feed your family.
edit: i'm stupid lol, kamaru usman and leon edwards are welterweight, not middleweight