It is a vanilla feature that paper disables.
To enable it you should change allow-piston-duplication to false in config/paper-global.yml
explosions are disabled and the only thing you can use them for is flying machines which why would you need a TNT duper for in the first place
how else would you make a cobblestone or wood farm except using wither which is less efficient and most likely doesn't work on the server either
This will clearly not happen, And just because exploit exist in vanilla does not make a feature
This is clearly a dupe
the only possible way that isn't complete garbage is getting a good pickaxe and making a good cobblestone generator
that way you can guarantee good efficiency, and if made well enough, you could afk farm it
They changed tnt to have 100 block drop chance a while ago, and a tnt cobble farm is the most efficient cobble farm tbf