My friends ps5 just randomly turns off only when he plays a PS5

So my friend just gave scalper price for a PS5 and it worked for a couple of months it tuned off one day and it wouldn’t play a PS5 exclusive game after it opens the game but after a few minutes it just completely turns itself off like all power just went off or something cuz it even throws the sign when you turn it back on that it wasn’t turned off correctly and we tested a couple of PS4 games such as mk11 PS4 version and brawlhalla a lite game and a somewhat demanding game so mk11 works for a hour or two then just shuts off on brawlhalla it has never shut off we took it to a repair shop and they said there’s nothing wrong with it and didn’t believe us when we said it turns off on PS5 games called a couple more shops around and one out of town but they all said the same thing basically saying they never heard of anything like that and accused us of lying to them or prank calling and or wasting they’re time so we are both out of ideas I always watched your vids so I thought you might be able to help any help is much appreciated