The LLAPI will no longer be shipped after 2019.4 (LTS), and will be supported for two years after this release. "The HLAPI will no longer be shipped after 2018.4 (LTS), and will be supported for two years after this release.
You do this within the OnSerializeNetworkView() function.You can still use UNet, the time before UNet won't work anymore has been extended due to a large amount of feedback.
If it is observing a Script, you must explicitly Serialize data within the script. Only the difference between the last transmissions values and the current values are sent and nothing is sent if there is no difference. All later packets are queued up until the earlier packet is received. If a packet is dropped, that packet will be re-sent. Packets are always received in the order they were sent. The data of the Observed Component will now be sent across the network automatically. To use State Synchronization, set State Synchronization of the Network View to Reliable Delta Compressed or Unreliable. You have 2 options to send the data of the Observed Component: State Synchronization and Remote Procedure Calls. RPC calls just need a single network view present so you don’t need to add a view specifically for RPC if a view is already present. If you are not directly sending data, just using RPC calls, then you can turn off synchronization (no data directly sent) and nothing needs to be set as the Observed property. You can select a Component from the drop-down, or you can drag any Component header directly to the variable. Whatever the Observed Component is, data about it will be sent across the network. This can be a Transform, an Animation, a RigidBody, or a script. The Observed property of the Network View can contain a single Component.