I tried a gold farm in a flat world to test it under the coordinate y 0. The farm did not spawn any zombified piglins as apposed to the gold farm I tried in a default world. I’ve tested this on both windows 10 and xbox one.

The way the farms work it to turn a portal on and off with fire and water. This is supposed to spawn zombified piglins.

I currently don’t have any visuals to demonstrate, but try this yourself in a world. I have not tested the specifics of what y level they spawn and don’t