Does anyone know what this is, or what might have caused it? My screen isn't damaged, and the only thing I've ever used to clean my screen was a damp fiber cloth towel. Any ideas? Thanks in advance.https://gyazo.com/49f7d7060674e822d2122161961251c3
No screen protector on the screen (that you might have installed?)
If not, then you just have some de-lamination on the display.
You fix that by replacing the display.
Honestly, looks like it's on the surface and something you can clean off with a really good wipe. Hard to tell on just a picture, but it doesn't look like the ant-reflective coating issue that I've seen a lot of... that usually looks more purple to the eye.