With the wheels on the ground, gently rock the car back and forth while applying light pressure to the gear stick to help pop it out of gear.
Internal components like the interlock balls or shifter forks are physically stuck. 2. Preliminary Attempts to Free it freetranny
A transmission usually sticks because the shifter rods, detent balls, or synchro collars have oxidized or settled into a "locked" state. With the wheels on the ground, gently rock