It's Samsung's way to earn, business model. My m31 handset too got blue dark screen. Usually it says it happens after damage, but it's false. It happens because of bad software update sent by Samsung or bad hardware. Already chipset of m31 and that handset got breached one time during lock down. M31 set is full of errors. And Samsung has no solutions, you'll need to pay for their faults. And they won't even accept it. It's fraud in a sense.
It's due to poor manufacturing quality of Samsung but they won't accept that. Your only option is to replace the display. But I would suggest you to buy a new phone because it's Samsung and anyday you will face a motherboard failure too. So, repairing will be a waste of money.
Nb: Samsung employees and those who thrive shamelessly on the bread crumbs that Samsung throw at them will try to claim that it's due to physical damage.
Sorry, guys, I have to disagree with you. Except for the faulty update, 2 years ago, I haven't a day's problem with my M31. If you drop the phone, or water gets in, you cannot blame Samsung for it, right?
I differ from your view. The device I used had no such drops or water ingress problems. It was as good as new. Not even a scratch. Protected all along.
But one fine day saw a small blue patch at the bottom screen which eventually grew to the middle of the screen making the device unusable. A well-protected device getting that is surely a manufacturing defect which samsung won't agree.
