2 by 4 gate

block survival:door-2x4gate-aged · from game

Can be generated by (1)

Random-stack placeholders (placed in world-generated chests and similar) whose pool includes this. The chance is among that placeholder's results, not the chance of finding it.

Found in structures (5)

This confirms the schematic(s) contain this code somewhere, not where or how many times -- the per-instance block-entity decoding used for tapestries isn't run for every content type.