I’m making this icon with a base vector and white strokes with variable profiles (right image) and I wanted to unify them as a single object, so I expanded the strokes and used Pathfinder’s difference (left image)
They appear identical, and they should, I guess… But when I zoom out, the one I used pathfinding look like it bled or something like that.
How can I make it look like the original?
Zooming is only a preview inside Illustrator. What counts is how it prints or how it displays in the final use (web, app, …). My best guess for the effect that you are seeing is that Illustrator calculates the preview for strokes and for surfaces differently.