Stacked layer creeper farm

Creeper farm made of two materials, building blocks and trapdoors, stacked in layers high over the ocean. Each layer costs 484 building blocks and 356 trapdoors and nothing else. The blocks are meant to be farmed as you go rather than gathered up front, so trapdoors are the only thing you have to make before you start. Creepers drop off the platforms into a chamber where zombified piglins sitting in minecarts kill them with golden Looting spears, and a snow golem in front of the piglins keeps them angry enough to keep swinging. That makes it fully automatic, no autoclicker and no killing by hand. The rate scales with how many layers you stack. Java only, the creator runs a separate channel for Bedrock.

Put a cat in each corner of every layer. One builder used twelve across three layers and says that is what made it work properly.
The piglins climb out of the minecarts, go for the snow golem and kill it. One builder gave up after the piglins then started killing each other without dropping the spears back.
Piglins will pick a spear up to inspect it and then put it away instead of wielding it. Getting them to keep it as the held weapon is the fiddly part of the build.
It has to be snow blocks, otherwise the creeper blows up. The snowballs themselves do no damage, they only keep the piglins angry.
Two layers is enough for most people. One builder ran sixteen and got about two stacks in five minutes, which is no better per layer.
Cats do not come with you through a nether portal while you are flying an elytra, so move them separately.