The green halo is what looks like to me today without glasses. Myopia/Astigmatism does that "naturally"

Astigmatism gives an anisotropy to the distortion, so on one eye it's stretched vertically, on the other, stretched at an angle

Interestingly, I suppose I have become accustomed to that kind of halo effect in high contrast situations (either due to something about my eyes or glasses), so I had no clue that the image was manipulated. It just looked like "normal" to me, since I suppose I just assume that there will be a halo around that sort of object.

I was only able to observe the halo effect added from the image manipulation when I physically blocked my view of the "O" with a piece of paper, stopping at the edge of the character. When only viewing the black area the modification became obvious: there's a gradient around the "O" which fades to black.

So the good news: it may not be anything about your monitor. The bad news: it may be your eyes! :)

Yes, it has been manipulated to add in a halo that corresponds to my post-lasik halo.

It is not that strong, but you can check with a color picker app or with a paint program that yes there really is one there.

I was wondering the exact same thing. It's not obvious to me that it has been manipulated at all.

There's a greenish halo around it, but it's very subtle.

If yoiu cant see it, it's likely down to your display being miscalibrated/shitty.