There is a checkbox in the customize menu to show or hide the backpack when an Elytra is equipped, it would be great to also have an option to hide/show one's own backpack in general, thanks!

It occurs to me now that Curios has a visibility toggle on each of their slots, so I am unsure if this suggestion is still worthwhile.
That said, I will leave this open incase it would benefit some use cases (such as those with capes who wish to ensure the backpack is never shown), but feel free to close it!