The MacBooks from the 2015 era have a design fault where the anti-glare coating rubs off, leaving a very messy display. It’s most obvious when the screen is dim. It look terrible! Flaky. Dinted. Stained. Scratched. The glass screen is actually still in tact. It’s just the anti-glare coating that has rubbed off.
You can read about the history of the problem, including Apple’s response, here.
There are various articles that describe how to fix it:
After reading these I did a repair, and here are my comments.
What you need to to do is remove the anti glare coating.
An alcohol swab like this works very well, and for me removed about 80% of my coating. I just rubbed it in circles with my finger.
There were some stubborn parts of the coating that the swab did not remove. For those parts I used some bicarb soda dampened with water and rubbed it in circles with my finger. I could rub with a fire amount of pressure, and it’ didn’t scratch the screen. I needed to be careful not to drop the bicarb soda onto other parts of the computer. It was a bit messy.
Here’s my results:
The screen looks great without the coating. Much better than with the flaking coating still on.
There is a lot of glare (see above) but when the screen is on you don’t really notice it.