Actually, I think The Phantom Menace was shot in 35mm, while framed for 2.35:1 and only ever presented in that fashion (and the only Prequel to even be shot on film), it may be the lone standout Star Wars film to have been matted and therefore have more picture to offer. You’ll never see that happen, and frankly who wants to see any more of TPM, but the material may exist out there somewhere.
Just to be clear, it is a rare circumstance where those black bars are hiding anything, and on the cases where they are, the covered footage usually was not intended to be seen and would be less polished than the portion originally framed for (especially in SFX heavy films, as there’s little reason to perfect effects in parts of an image not intended to be seen). Take 4:3 “Fullscreen” video (or “Fullframe” older films), on a modern TV you see black bars on the side, you can’t believe there is video they’re hiding on the sides (well, except for movies that WERE widescreen and then cropped in the CRT era to “fit your TV”), in that same way there’s not likely something hidden in black bars at the top and bottom of an extra wide video presentation.
TPM was shot using Arri cameras and 2x squeeze anamorphic Hawk lenses.
https://www.theasc.com/magazine/sept99/phantom/fx2/main.htm
Therefore all live action is not matted (only Super35mm/VistaVision/70mm can be properly hardmatted to 2.35 and maintain picture quality) and what you see on the screen is pretty much on the film frame (apart from some very light cropping around the edges). There’s nothing hidden.