What exactly is flexgate on MacBooks?

Apple's service program for the 13 inch ran for a fixed number of years after purchase, so if yours is only failing now it's almost certainly out of it. Worth asking anyway, but expect to pay. Two things that can save money: some independent repair shops will replace just the cable instead of the whole display, which costs a lot less. And until it's fixed, don't open the lid all the way, staying under the angle where it cuts out slows the wear down.

Nickname for a display fault on the 2016-2017 MacBook Pros. The flex cables running from the logic board to the screen were very short and got bent every time you opened the lid, until they wore out. First sign is the 'stage light' look, uneven bright patches along the bottom of the screen. Later the backlight cuts out completely once you open the lid past a certain angle. Apple ran a service program for some of the 13-inch 2016 models, and later models came with a longer cable. Fixing it outside that usually means replacing the whole display, which is why it's pricey.