The only person that I know can do this is Astrauwu, and it's shown in the RS All Armor Sets run. I can only do the insta-mine. I know the glitch includes naming a chest by pressing n, but whenever I do exactly what Astrauwu does, my item doesn't get duplicated. It's probably the most complicated glitch in the history of Scratch games.

Place the chest, put you item in the bottom middle slot, name the chest, open inventory or crafting table, take the item, repeat.

Thank you so much! 2b2t style duping lol