I'm just thinking that duplication wasn't a part of Minecraft when I saw this video in my YouTube recommended:
A lot of resources in Minecraft can be farmed - produced in large amounts with very limited player input, occasionally entirely without player attention. You don't really need carpet duping - a proper automatic sheep farm supplied with enough shears will give you more wool than you'll ever need.
Other than that, there's a couple bugs - glitches - that allow duplication of resources.
Carpet and rail dupe are particularly persistent, every version Mojang tries to patch them only for them to reappear in a new form. There is hope it will get patched for good, but no guarantee - implementation of correctly moving these blocks by pistons is tricky.
Gravity block duping using End portals is well-liked by the technical community, as it provides renewable sand, and the effort-to-reward ratio is relatively high, a proper efficient sand duper quite comparable in difficulty to legit farms producing similar amounts of more valuable resources.
There's TNT duping (without generating the item or block, just creating a lit TNT entity without using up the block) which is a bug that was patched in 1.13 snapshots only to be rediscovered a couple snapshots later in a new form - and this dupe is currently declared by the lead developer to stay until a "legit" alternative is implemented, as the usefulness of it is very high - it allows automation of breaking blocks - automatic tree farms, cobblestone and basalt generators, quarries and world-eaters.
There's a general block dupe using update suppression - a bug that is difficult to fix, as it depends on the player overloading the server's stack and triggering an anti-crash safeguard, aborting normal processing of in-game events - in particular after producing an item drop, the server is forced to abort execution before the block is removed. Regardless, the effort to reward ratio in this case is pretty poor (the update suppressor machine is massive) and Mojang will attempt patching the exploit sometime soon anyway.
And in the end, the only true general item dupe - the infamous 'Donkey Dupe" from 1.15 and earlier - allowing duplication of entire shulkerboxes of goods - has been patched in 1.16, but the patch is flawed; methods of exploiting it still exist although unreliable and difficult; doing it without a hacked client is nearly impossible. Hopefully a better patch will be implemented.
As of 1.16.5 no other duplication exploits in Java Edition are known to be present. A number of past exploits have been removed, in particular hopper dupe and llama dupe (from 1.12 and earlier), drowned dupe (1.13-1.14), and baby piglin dupe (1.16.1-1.16.3) have been patched.