in this build the only shader doing any work is one that locks the colors to the two-color palette (to catch any stray alpha pixels, or mistakes in my pixel art, like using pure black & white instead of the tinted palette)
The bulk of the effect is simply from having this overlay, which i made at a higher resolution than the game's actual pixel art
I just used Aseprite's dithering radial fill
This creates the effect of dithering sub-pixels basically, the further from center screen, the darker the pattern.
The last trick is swapping objects' layer from behind to in front, so i can selectively disable the dithering on certain objects
This is how some of the raw pixel art looks:
