Okay, this shit happens. I lived it for a decade.
MacBooks tend to have monitor issues due to the hinge and cables being all together right there at the vent in the back. It’s a pain in the ass, because they improved (read: fixed) it when the SSD version of the MacBook launched a LONG time later. It’s also a pain to fix, because I had to take the ENTIRE display and hinge apart to adjust or fix ANYTHING other than hard drive, RAM, or battery on that bastard. I used to HATE regular MacBooks because of that bullshit. Give me a MacBook Pro any day, much easier to repair.
Apple draws a line when it comes to their technology and software updates. They are aware what their hardware can take, and try to draw the line at a (somewhat) reasonable spot at which the hardware just can’t handle it without major speed issues. Typically, with a Mac, it’s at the 6-8 year mark (which is generous, given how fast technology moves). With the phones, it’s normally at about 5 years (again, pretty damn generous, knowing how phones are basically disposable at this point).
iOS 13 doesn’t exist anymore, because they have moved on past it to iOS 14. (They have announced iOS 15 already, but haven’t released it in the wild.) If you miss too many updates with iOS, you wind up in this kind of situation. My recommendation is to get you phone updates at a store (which will do it for free). Just remember to (and I CANNOT stress this enough) back up your shit up first.
If it’s just the monitor that is broken, you can get the display, back panel, and hinge repaired. Downside to this is that the repair itself is usually 50-85% of the cost of the unit. Check to see if you have any repair places close to you that have parts available. You might get lucky. Also, back up your data before the repair.