2018 acadia car does not register it is in park and cannot be shut off
It’s still under warranty, take it to the dealer.
Does it seem to be in park with P selected? Does it seem to want to move when you press on the gas in P? Does it seem to shift into N correctly? Per the post above, don’t try to fix this, let the dealer do it. But knowing the results of the above experiments might help the dealer solve it.
Put a power point in a 2017, tapped into an ignition source for a 2 way radio shut off with ignition, believe it or not van would not shut off if the power point had a spotlight plugged into it. Any after market stuff?