Look on top of the transmission and see if the cables appear to be broken or disconnected while somebody shifts the shifter around.
The ends on the shifter cables tend to break because they're made of plastic on many cars and that causes this. The end is available separately from the dealer for like $12.
You don't need to take it to the dealership for this, it's super easy to fix if it's the cable ends and I can describe how to fix it. You literally just need a drill bit to replace cable end and set the shifter.
The dealer is going to charge an hour to diagnose this and then like another hour to replace the end and set the shifter. So like $230.