So, any salesman or dealership blaming this on chip shortage is uninformed. It's simply a cost cutting move.
I set out to add rear passive button handles on my 2024 1500 Denali. First, none of the necessary wiring is in the truck, in either the door harness, or the body harness. The (passive) rear door handles have two wires. One is ground, the other is 7v signal. The button simply grounds the signal, telling the module to check for FOB and do it's thing.
With that said, I have successfully added a rear passive entry handle on my driver side rear door. The other handle is on order. You will need to remove the door panel, the center pillar panels, drivers kick panel, etc. The ground wire for the button can be tied into the door harness ground, and the signal wire will have to go tie in to the drivers passive button wire. On my truck it is pin 17 (blue wire) in the driver door, door/body harness.
If I hadn't been so used to having the rear buttons on my '20 AT4, I probably wouldn't go through the trouble of adding them. However, I constantly find myself trying to push the button to open the back door, only to have to reach to the front door.