I've had this happen to me before. I stopped hard and put it into Park and couldn't shift after that. The problem was the Neutral Safety Switch and the cable attachment. I rocked the car back and forth while rocking the cable attachment. This worked for me as something "released" and I was able to move the shifter again. I posted about it here a couple of years ago if you want to search. I think it was titled "Help! At work car won't shift" or something like that.

Good luck!

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2009 R350, now the daily driver
1980 300SD, was the daily driver