I've noticed this for years... whenever I create a new document in Illustrator--no matter the size or mode and without any bleed settings, the artboard has a tiny grey "drop shadow" behind the artboard. See ATTACHED (top left and top right corners). It does not affect art and never prints, but more times than I can count I've found myself zooming in and attempting to select/delete it, thinking I left some sort of unwanted element behind while I was working. Or I see the faint "border" and think my graphic elements aren't fully aligned to the page edge, when the actually are.
It seems like it's just a "cutsie" little unneeded addition to the artboard. Does anyone know of a way to get rid of it? I've poked around in preferences and View settings but couldn't find anything. Or maybe I need to (somehow) complain to an Adobe "ideas/complains" thread? Thanks. Using Illustrator 2020 on Mac OS, but like I've mentioned, it's been there for years, perhaps decades.