From what I recall from the light novel, the High Human race only belonged to the six devas (the six most powerful people in the game, Shin being one of them). They are different than other races with the "high" name such as high elves and high beastmen. I believe it's because regular humans had such a short lifespan compared to regular elves/beastmen and so to become a high human they had to reincarnate (while this was still just a normal game) while regular elves and beastmen can train themselves up with their long lifespan (again, only while they were in the regular game). There hasn't been and explanation as to what exactly humans need to do to reincarnate into high humans as of vol 12 of the light novel.
Remember, there hasn't been any more high races since the Dusk of Majesty (500 years ago when Shin beat the game). So that's why when other player's supporters see Shin, they give so much respect to him. He is the one who basically "saved" the world by beating Origin.
Also Shin is just OP with his limit breaker title on TOP of his already maxed out stats. When he fought and beat Girald, his supporter, he told Girald's grandson and great grand daughter to be proud that Girald's last strike actually hit him, a high human.
Edit: If Shin was seriously mad and didn't care about consequences, he could probably just go all isekai and destroy whatever he wants and no one would be able to stop him at all. Not even the other players here that we see him meet. This chapter introduces us to the other part of Shin where he was the "Grim Reaper", killing off other PKers