Hi
I’ve had the same issue, bought the console from launch, so had it just over two years now. I had it looked at by a tech engineer and they’ve essentially said the graphics card is damaged, so it will play lower resolution PS4 games as they are less demanding on the system. Unfortunately, the graphics card is part of the motherboard and can’t be replaced, Sony won’t even be able to fix it. I have asked the retailer to replace my console, which they of cause refused to do as it’s out of warranty, but have agreed to a pro-rata refund. The alternative option is to use Sony’s out of warranty service, which costs £240, but they guarantee to give you a working console- if they have a refurbished one then that’s what you get, otherwise they provide a new one. You may need to get someone to independently look at your console and investigate the cause of your fault, but I’ve seen plenty of cases online exactly the same as mine.