Won’t start and stuck in Park

  mercedes/glk-class/2010-____

I have a 2010 GLK 350, love the car! 70k miles, got it used, it’s had reg maintenance.
Yesterday I pop into the mall, 20 min tops, come out and she is dead. My alarm works, the overhead lights and dash turn on, but that is about it.
I called a tow, but she was stuck in Park, we jumped, twice from the tow truck. No change.
There is no turn over, no noise, no flashing lights, and no signs leading up to the issue.
I found the button under the gear shifter boot to release the car to neutral!! Yay, I got her towed. But now I’m left with a dead car.

Any ideas? I towed it home, can run a few tests from here, with some of your help, please and thank you!!

CC

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