There's a halftone screen here, and that's the explanation. The Exported version is correct, the preview is wrong.
For this, you must view at 100% to get a correct preview. In Photoshop, 100% has no relation to size. It means one image pixel is represented by exactly one physical screen pixel.
To speed up preview rendering, all adjustment and blending previews are calculated on the basis of the on-screen image. When you are zoomed out, that's a downsampled and softened version. All those halftone dots are blended and smoothed into intermediate values that aren't there in the original. So the preview is misleading, because the calculations have been made on "false" values.
When all the layers are flattened for export, those layer calculations are performed on the full and complete pixel data, pixel by pixel.
By viewing at 100%, those two are one and the same, and there is no discrepancy. What you see is what you get. Always make it a habit to check at 100%. This doesn't matter for a "normal" photograph, but it becomes absolutely critical when you have halftone dots, line art, finely textured graphics, very noisy images and so on - anything that has very sharp pixel transitions.