Portal drop creeper farm

Creeper farm with cats and nether portals, 25000 gunpowder an hour from a build one player can run. Creepers spawn on stacked platforms, cats sitting on each platform scare them off the edge, they drop through nether portals into a killing chamber, and you swing a looting sword at armor stands to kill them. Hopper minecarts underneath collect. A lightning rod stops storms turning the creepers charged. It is a long build, ten hours or more by builders' own accounts, almost all of it the 4880 trapdoors, which the creator suggests getting from unoxidised copper in trial chambers at two trapdoors per copper block. Java only. The beacon is there so you do not starve while AFK, which the creator says is necessary on hard and recommended on the rest.

Several builders confirm 26.2, one of them on a paper server. Bring about 20 slabs more than the list says, plus ladders and an ender pearl for the nether roof.
Some creepers jump diagonally and land on top of the nether portals. One extra trapdoor on each side where they jump fixes it, or magma blocks on top of the portals if the farm is already built.
Put torches on the corners of every platform while you build so creepers do not spawn behind you, then take them out one at a time at the end.
Do not put knockback or fire aspect on the sword. Knockback pushes the armor stand out of place and fire aspect burns it.
On a server with a low render distance you need a second account AFK at the platform below the storage.
Build the modules exactly as shown. One builder made 3x3 modules instead of 2x2 across ten layers and got almost no spawns.