Lava drop iron farm

Iron farm for 1.16, three villagers and one zombie, small enough for an early survival world. The villagers try to sleep in three beds, a zombie standing on a fence post above them keeps them scared, and the golems spawn on the platform and fall into lava. Seven hoppers underneath carry the iron and the poppies to two chests. There is no redstone and nothing to power, so the only real work is bringing the villagers in on rails and getting the zombie into place. The design is MineTheFab's, this video is the tutorial. Java only, and only up to 1.16.1, because 1.16.2 changed how villagers get out of bed and the creator pinned a note saying it stops working there.

The materials list is missing one fence, the post the zombie has to stand on. The creator confirmed it and never added it to the description.
Put a trapdoor above the zombie's head, and name the zombie with a name tag or it despawns.
The villagers have to sleep at least once before you scare them, otherwise the farm never starts producing.
Leave no blocks under the beds, and make sure the golems fall on the villager side. On the zombie side he hits them in the air.
Build it at least 150 blocks from a village. The creator gives 150 in one reply and 70 in another, so take the larger. Farms tile side by side with 14 blocks between them, never stacked on top of each other.
For 1.16.3 one builder got it working by filling the gap between the three slabs with a trapdoor, which stops the zombie converting the villagers.