>>19828142 (OP)"undo" as in "go back to the original"? Nope. The information is destroyed. An artist or an ai could paint in something that looks plausible, but the actual picture is gone.
If you've heard about undoing pixelation recently, that's on video data. If you have blocky pixels which change their colors as the uncensored picture underneath is moving across the pixel boundaries, you can draw conclusions about that underlying picture. That doesn't work with a still.