funky stuff going on with display

this macbook works fine hooked up to an external display, but it's built in is only backlit. The built in is the original built in display from another macbook of the exact same make and model. In the system info app i can tell that the computer recognizes the fact that the display is here and it is connected into the display, there isn't an error showing and i'm confused. I guess what I am wondering is why i can see everything totally fine on an external display, but i only have backlight on the built in, with no errors showing?? Thank you!

I would like to add that I’m using the exact macbook on an external display to write this.

Also - this exact built in screen when it was on its original computer before I put it on the one I'm on now, it had the same issue, I moved it over because I thought it was a software thing.

here is a picture of it