One problem might be the nitwit. I'm not sure if they can contribute to the generation of iron golems because they don't work like other villagers. Also, in the photo, the villager on the right doesn't look like a fisherman...he's not got the hat of that profession. Perhaps he's attached to a different workstation.
One other thing: You need to move your farm up into the air. If you leave it on the ground like that, you will most likely spawn golems next to the villagers on the grass and it might go kill the zombie.
Any idea why is it not working at all...
This farm is made in 1.14.4 on online server of mine. I have redstone clock hiding zombie so they can go to bed and use their work stations.
hlp
I'm not really clear on the current village mechanics but could it be that the villagers have to be closer together in order to gossip?
The standard design seems to be to have 3 villagers, beds and workstations in one cell, and at least 2 such cells.
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Also the Wiki claims you need to have at least 5 villagers within 80 blocks of each other.
Just testing.
I don't know man i did the design from internet and it was working on video so...
One problem might be the nitwit. I'm not sure if they can contribute to the generation of iron golems because they don't work like other villagers. Also, in the photo, the villager on the right doesn't look like a fisherman...he's not got the hat of that profession. Perhaps he's attached to a different workstation.
One other thing: You need to move your farm up into the air. If you leave it on the ground like that, you will most likely spawn golems next to the villagers on the grass and it might go kill the zombie.