First I would pull shift bezel to check if anything got down in there and is physically impeding the selector.

Then I would look under the car and watch the linkage move to see if it is obstructed somehow.

Have someone give you a hand... and don't have the car running lol.
The linkage is in plain sight on the driver side, mid tranny.

I wouldn't think that it could be anything internal to the tranny, my bet is up top.