hi I am in photoshop v22.2 on Mojave and learning export as now and seem to be unable to find any descriptors online of the funtion of the small half white - half black circle icon/button just to the left of the zoom in toggle in the center bottom of the export as tool.
I am guessing its an on and off toggle switch for seeing changes in resampling choices, but they are barely perceptibly differences if any so just want to get someone else's eyes on this.... thanks - dan
It darkens the transparency checkerboard so that you can see it more clearly especially if the image has a white border or background. It's a "toggle" button. You can click it on or off, but oddly the button does not change, only the preview.