I would like to move a chair and a player mounted on it smoothly on the client side. I currently set a timer that triggers every 1/120th of a second on the server that translates the player and the chair by a fixed amount. The movement looks stuttery on the client side. I tried adding a Rigidbody to the chair, set isKinematic to true to both the player and the chair then set the velocity. That didn't work. The chair remained in the same position. I think I need to send the changes I made on the Entity to the clients but I do a SendNetworkUpdate every 1/120th of a second so that shouldn't be the issue.

Any help would be appreciated.

Even with super frequent updates, the movement will be stuttery unless the client interpolates the movement of the entity. The only way to achieve client interpolation is to use an entity that the client is hard coded to interpolate. For example, spawn a sphere entity, and parent the chair to that. Movements that the sphere makes will appear smooth, as long as the updates are frequent enough. You can probably use InvokeRepeatingFixedTime method with NetworkPositionTick for this. That is how I solved it in Drone Scale Manager.

Also make sure that the entity you are moving (i.e., the sphere) has a rigid body, or the movements will likely cause lag, as per Unity behavior with moving colliders.