If you put a light block above sugar cane, cactus, or chorus fruit, it prevents them from growing. It also prevents dispensers from dispensing carved pumpkins onto iron/snow golems. Whenever you normally place a block on the light block, it replaces the light block instead.
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is duplicated by 4
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Note that it doesn't prevent the growth of fungus, see MC-222761.
So I don't think it's intended.
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This also affects noxious gas and geysers, see MC-307958
Can confirm, but this is probably intended/feature request. This is also very useful, they are a good replacement for strings when it comes to preventing crops from growing, so please keep it.