I tested this on my Model Y today. 12V battery is fine. When the car is locked, 12V to the jumpier leads does NOT open the frunk. I did turn off Bluetooth on my iPhone for this test. When the car is unlocked, 12v to the jumpers does open the frunk. This is exactly what the owner's manual says it will do. I assume the jumper thing will work if the 12V battery is dead, as that is what the jumpers are for.
Mine is a 2021 Model Y, LR, Software version 2021.4.48.
SW