What blocks are iron golem spawn proof?

Iron golems don't spawn in lava, on bottom half slabs, on pressure plates, transparent blocks(They can on those covered with water!), on magma blocks, and on blocks with wierd hitboxes (Lantern...)

Glass Blocks, Grass Blocks and Strings from spiders are spawn proof! I tried it and it worked for me!

1.16.1:

Iron Golems are still spawning on half-slabs and glass for some reason. I covered the glass with buttons and carpet and so far no golems have spawned on the glass.

I kept having issues where they would spawn on the glass and kill my zombies that are agroing the villagers. After placing carpet and buttons, I have no issues.

I'm using this design:

Placing carpet worked for me! Glass block works as well.

STRING! They're cheap and effectively work on any block you'd like and do obstruct the 3 blocks of vertical space above any block that iron golems require to spawn. They can be stacked on top of each other as well, which allows them to be used anywhere, and don't clutter your view too much as they're virtually invisible.

Other blocks that could work, if you prefer them, are redstone dust, signs, repeaters, buttons, pressure plates, torches and comparators, for example. Essentially most non-solid blocks (I'm not sure about ALL) can be used to obstruct the spawning of the iron golem.

Using glass or chests as floor blocks also disallows iron golems to spawn, at least in 1.15.2 (according to my lazy testing that is, tell me if I'm wrong).

Edit: Golems cannot spawn on bottom half-slabs either.

only plugging the offending spots with solid blocks will stop the spawning.

NOTHING ELSE WORKS.

If there is no 3 high clearance except where you want them to spawn, you are good. Since lighting no longer affects house detection, this is somewhat practical to do now.

Mojang doesn't want you trading with the villagers and farming iron golems at the same time anymore.

It's a real shame, i had an awesome pre village and pillage design that spawned golems reliably in the middle and had the villagers arranged in a square around the spawning area in their own little compartments with pricing signs. This cannot be done ever since village and pillage. Mojang has borked every workaround i've had working in the next patch.

Glass has worked for my farm so far I've changed it about 10 minutes ago after my golems were spawning on my half slabs changed it to glass and everything has spawned in the place I need it to including cats

On the Minecraft Wiki, it says:

Mobs will not naturally spawn on transparent blocks, in water (except for squid, drowned, fish, dolphin and guardians), in lava, or on half blocks (slabs, stairs).

So I guess this applies to Iron Golems as well.

To check, you can create a superflat world, find a village, make sure it meets the conditions, and see if one spawns.