Minecraft Pick Block Duplication Glitch _VERIFIED_
The best way to duplicate a block is to turn it into an item first, then duplicate the item. However, there are other ways to duplicate the blocks themselves, though they only work for certain blocks. Shulker boxes make item duplication much easier because they allow for up to 1,729 items to be cloned at once (including the shulker box).
Minecraft Pick Block Duplication Glitch
This duplication glitch works on 1.16.5 multiplayer. It requires an elytra and firework rockets that deal damage to the player. If the rockets do not damage the player, the duplication will not work. Video below: (duplication glitch starts at 0:33)
The mechanism for growing giant spruce trees is known to be glitched in JE 1.16 snapshot. Instead of growing a giant tree on the saplings, the game grows the tree on the first position where space is sufficient and a dirt block is present in the north-west position. When the tree is grown, all the dirt blocks are filled in. With bone meal and piston automation, a semi-auto dirt duplicator can be produced (YouTube by ilmango).
This duplication glitch works on Singleplayer and Multiplayer. All you have to do is place a chest in front of you and then leave the server as it saves your player data, then relog and put the items you want to dupe from your inventory in the chest, get a book and quill, overload the book with excessive characters and it will cause you to get kicked from the server and rolling back your player data to last save while server files stay the same. As a result, the items will be in both your inventory and the chest. (requires fabric download and custom download to work)Video here:
These item duplications work in vanilla servers and Realms, but many servers use a modified server software called Paper for many reasons, including swiftly patching many exploits. Here are many block duplication methods that will not work on recent builds of Paper but work fine in vanilla.
TNT duplication works in a similar way as rail duplication. A TNT block is BUD-powered, such that when the contraption is pushed by a piston, the TNT is updated and ignites into a primed TNT entity. Then, the piston moves the TNT from the list of TNT block left. This doesn't so much duplicate the TNT block as it creates free primed TNT entities from it without deleting it. Many TNT duplicators still work, but unless properly constructed will blow themselves up.
One common TNT duplication design uses a minecart on a detector rail to power the slime block it is placed on, and moves a TNT block next to a coral fan underneath, the combination of the TNT and the coral duplicates the TNT whenever the whole contraption is moved forward with a piston. For an indepth tutorial of this one checkout Cheesysponges video
This dupe involves baby piglins. It is incredibly simple and it works in multiplayer. To perform this glitch find a baby piglin and drop his health down to a 1-hit kill (2 hits with a normal diamond sword should work). Then drop the item you want to duplicate to the piglin(e.g. a shulker box) then wait for the baby piglin to pick it up. After the piglin has picked up the item drop the piglin 1 gold ingot. While the piglin is admiring the gold, kill the piglin.