Forecast Disabled
Forecast Disabled synchronizes physics objects from their authority to other clients in the same way non-physics objects are synchronised. On proxies, by default, their rigidbodies are set to kinematic, so that all physics interactions are handled on the authority. See Physics for an overview of the alternatives.
It suits non-interactable physics, for example where characters can not push physics objects. The proxies are in remote time. If physics interactions are enabled, they will not, in general, be smooth.
Fusion 2.0 Compatibility
The behaviour changed in Fusion 2.1 from Fusion 2.0, which did not set proxy rigidbodies to kinematic. To behave identically to Fusion 2.0, set the property NetworkTransform.PhysicsSettings.SetForecastDisabledProxyRigidbodiesToKinematic to false in code.