“I have already made my decision...”, which is not true at that point
It’s true in temporal sense, just not true in the more general acausal sense, where even in Transparent Newcomb’s Problem seeing the contents of the box doesn’t mean that the contents of the box are already-acausally determined, since being determined in this case refers to the (logical knowledge about the) distribution of states of the box in the possible worlds, not to the (knowledge about the) state of the box in the world you’re observing (you don’t even properly know which world is that at that point, so can’t use the observation to refine the model that describes the possible worlds under study, so long as you work with all of them, without updating away those inconsistent with observations).
It’s true in temporal sense, just not true in the more general acausal sense, where even in Transparent Newcomb’s Problem seeing the contents of the box doesn’t mean that the contents of the box are already-acausally determined, since being determined in this case refers to the (logical knowledge about the) distribution of states of the box in the possible worlds, not to the (knowledge about the) state of the box in the world you’re observing (you don’t even properly know which world is that at that point, so can’t use the observation to refine the model that describes the possible worlds under study, so long as you work with all of them, without updating away those inconsistent with observations).