public CIMRenderer GetRenderer()

{
  // Note: the following should be embedded in a QueuedTask.Run() statement
  {
    // GetRenderer from Layer (assumes it is a unique value renderer)
    if (featureLayer.GetRenderer() is not CIMUniqueValueRenderer uvRenderer)
    {
      // not a unique value renderer, leave
      return;
    }
    //layer has STATE_NAME field if using the community sample Data\Admin\AdminSample.aprx
    string expression = "if ($view.scale > 21000000) { return $feature.STATE_NAME } else { return 'All' }";
    CIMExpressionInfo updatedExpressionInfo = new()
    {
      Expression = expression,
      Title = "Custom" // can be any string used for UI purpose.
    };
    //set the renderer's expression
    uvRenderer.ValueExpressionInfo = updatedExpressionInfo;

    //SetRenderer on Layer
    featureLayer.SetRenderer(uvRenderer);
  }
}

{
    //Note: Needs QueuedTask to run
    //Get simple renderer from the feature layer
    CIMSimpleRenderer currentRenderer = featureLayer.GetRenderer() as CIMSimpleRenderer;
    if (currentRenderer == null)
        return;

    //Set symbol's real world setting to be the same as that of the feature layer
    symbol.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

    //Update the symbol of the current simple renderer
    currentRenderer.Symbol = symbol.MakeSymbolReference();
    //Update the feature layer renderer
    featureLayer.SetRenderer(currentRenderer);
}

{
    //Note: Needs QueuedTask to run
    //Get simple renderer from the feature layer
    CIMSimpleRenderer currentRenderer = featureLayer.GetRenderer() as CIMSimpleRenderer;
    if (currentRenderer == null)
        return;
    //Get symbol from the SymbolStyleItem
    CIMSymbol symbolToApply = symbolStyleItem.Symbol;

    //Set symbol's real world setting to be the same as that of the feature layer
    symbolToApply.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

    //Update the symbol of the current simple renderer
    currentRenderer.Symbol = symbolToApply.MakeSymbolReference();
    //Update the feature layer renderer
    featureLayer.SetRenderer(currentRenderer);
}

{
      //Get the ArcGIS 2D System style from the Project
      var arcGIS2DStyle =
Project.Current.GetItems<StyleProjectItem>().FirstOrDefault(s => s.Name == "ArcGIS 2D");

      //Note: Needs QueuedTask to run
      //Search for the symbolName style items within the ArcGIS 2D style project item.
      var items = arcGIS2DStyle.SearchSymbols(StyleItemType.PointSymbol, "Circle 1");

      //Gets the CIMSymbol
      CIMSymbol symbolToUse = items.FirstOrDefault().Symbol;

      //Get the renderer of the point feature layer
      CIMSimpleRenderer renderer = featureLayer.GetRenderer() as CIMSimpleRenderer;

      //Set symbol's real world setting to be the same as that of the feature layer
      symbolToUse.SetRealWorldUnits(featureLayer.UsesRealWorldSymbolSizes);

      //Apply the symbol to the feature layer's current renderer
      renderer.Symbol = symbolToUse.MakeSymbolReference();

      //Apply the renderer to the feature layer
      featureLayer.SetRenderer(renderer);
  }

{
    //Note: Call within QueuedTask.Run()
    if (MapView.Active.Map == null) return;

    //Get an existing Layer. This layer has a symbol you want to use in a new layer.
    var lyr = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>()
          .Where(l => l.ShapeType == esriGeometryType.esriGeometryPoint).FirstOrDefault();
    //This is the renderer to use in the new Layer
    var renderer = lyr.GetRenderer() as CIMSimpleRenderer;
    //Set the DataConnection for the new layer
    Geodatabase geodatabase = new Geodatabase(
      new FileGeodatabaseConnectionPath(new Uri(@"E:\Data\Admin\AdminData.gdb")));
    FeatureClass featureClass = geodatabase.OpenDataset<FeatureClass>("Cities");
    var dataConnection = featureClass.GetDataConnection();
    //Create the definition for the new feature layer
    var featureLayerParams = new FeatureLayerCreationParams(dataConnection)
    {
        RendererDefinition = new SimpleRendererDefinition(renderer.Symbol),
        IsVisible = true,
    };
    //create the new layer
    LayerFactory.Instance.CreateLayer<FeatureLayer>(
      featureLayerParams, MapView.Active.Map);
}