The driveshaft flange on the tail of the trans has been known to wear out the splines and leave you driveless. However, the car will roll in park if that happens.

Did you elevate the drive wheels and see if the car will run forward / reverse? Many times a elevated car will drag the drive train forward in neutral so don't be concerned.

There are a few other possibilities.

The manual valve became detached from the shift linkage ( pull the pan off to inspect )

Pressure regulator spring failed reducing line pressure. There should be a pressure test tap on the outside of the trans.

Some transmissions will wear out splines in a drive shell, teeth from the friction plates leaving it drive less. I'd have to dig through the apply charts to determine if a singular failure can cause all loss of drive in both directions.

Did you move the shifter to different positions? Sometimes an overrun sprag will fail and the manual lever must be moved to that specific gear to engage other clutches. ( On some trans, 1 st ( or other gears for that matter ) gear in drive provided no engine braking becasue it is driving from the sprag. If the shifter is moved to that specific gear, engine braking on overrun is provided. )