I think most of the getter/setter functions have been changed to properties. So instead of mob.set_linear_velocity(Vector2(10, 10)), it would be mob.linear_velocity = Vector2(10, 10) for example.
It may be the Your First Game tutorial has not been updated with the changes, and/or it was missed when the tutorial was updated (having made a few tutorials, it's really easy to miss things like this)
