I need help creating a wearable backpack in MCreator 2020.5

I am not entirely sure you can do that without some code

you can make a custom modeled armor in blockbench which represents a backpack. make the gui, make a keybind and a procedure for that keybind for the backpack to be opened when you wear it.
i found a vid in yt that follows my recommendation

heres the link: https://www.youtube.com/watch?v=F1yE1dQmu3Q

hope this works