Since a while ago the preview window stopped showing the file sizes for all my assets. I can’t see any option anywhere to turn it back on. Is this a bug or did I disable something?
Make sure you are viewing the original image texture from the Textures folder (or wherever it is placed), instead of clicking on any button, material, or any other gameobject where the texture (or sprite) is added.
I had the same issue just around a week ago, where the image size was not visible even when I viewed it from the original Assets folder. What I did was I clicked on that 3 Dots next to R G B (top right corner in your image), selected “Minimize in Inspector” and then clicked on that dots again and selected “Restore in Inspector” and it worked somehow. Not sure how.
I have exactly this problem … 