If you will place the structure void, and then try to destroy it, the block behind it will be destroyed. If you will hover over it, it won't be highlighted. Also, you cannot place any blocks on it.
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[MOD] GoldenHelmet, i don't think it's intended because in 1.20.1 (the latest release), previous versions and Java Edition it can be destroyed.
Probably intended because the purpose of structure void blocks is to mark air/empty space in a structure that should not overwrite pre-existing blocks when the structure is generated/loaded. They aren’t meant to be interactable in any way.