public sealed class Spawner : NetworkBehaviour
{
    [SerializeField] private GameObject _prefab;

    [Button]
    private void Create()
    {
        var instance = Instantiate(_prefab);
        instance.GetComponent<PredictedSpawnTest>().SetScale(Random.value);

        InstanceFinder.ServerManager.Spawn(instance, Owner);
    }
}

public sealed class PredictedSpawnTest : NetworkBehaviour
{
    private readonly SyncVar<float> _scale = new();

    private void Awake()
    {
        _scale.OnChange += OnScaleChange;
    }

    [ServerRpc(RunLocally = true)]
    public void ServerSetScale(float scale)
    {
        _scale.Value = scale;
    }

    public void SetScale(float scale)
    {
        _scale.Value = scale;
    }

    private void OnScaleChange(float prev, float next, bool asserver)
    {
        transform.localScale = Vector3.one * next;
    }
}