If an item frame has been placed face-up on top of a block, e.g. top of grass block on ground, the player can extend redstone trail through item frame that was placed on ground, when clicking on the block on which the item frame was placed on top of.
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Item frames are entities, they can occupy the same space as certain non-full blocks (which is intentional as per MC-244176 being triaged). Resolving as WAI.
Item frames aren't blocks, you can place every block at the same position.