In the mobile dispatch when you us "bulk assign" (new feature to assign several tasks at once) it doesn't assign the whole order (pickup and all dropoffs)

[Atala]

It would be useful now for lastmile as the dropoff can be far from the pickup.

As the app stands, it is indeed not very practical to split orders between riders in-app. If one really wanted to do so they could assign the whole order, then unassign one of the tasks and re-assign it to a different rider.