So if you go on singleplayer Minecraft 1.15.2 or less (could be in 1.16) and and take a campfire (in survival) and take the items that you want to dupe. (must put render distance and everything and fancy etc.)then you go on the campfire and wait untill you dou are on like 2.5 hearts and leave the game and join backin in the same world (rejoin)then you die and DONT click the Respawn button but you click Ctrl + Alt + Delete and go on task manager and close minecarft and then open the Minecraft launcher and it will say GAME CRASHED if you join the world the items what you wanted to dupe will be laying on the GROUND and in YOUR INVENTORY