The keybind should work while vanilla player inventory is open like the original Curios mod.

I just started a new 1.16.5 world and updated this thread. what I noticed is:

If keybind activated while vanilla player inventory is open, the curios side-panel opens. (different than this mod)
If keybind activated while curios panel is open, the entire inventory screen is closed. (same as this mod)

Players could replace the vanilla inventory button with the curios keybind but it takes up a lot of space and cuts into JEI/EMI