We consider the System.Windows.Forms.DataVisualization deprecated and we only provide it to ease porting to .NET Core 3. We're not going to innovate in this component and subsequently will not accept any issues and/or PRs.
You're welcome to fork the source, and update it as you see fit.
This repository contains partial source code of the System.Windows.Forms.DataVisualization namespace that provides charting for WinForms. We ported and open sourced those components to enable charting features for WinForms applications that are developed on .NET Core 3.
The best way to learn about Chart Controls is by looking at the sample solution where via interactive experience with the app you can learn about every chart type and every major feature. While modifying the control parameters and instantly seeing how that affects the look of the control, you can also get the generated C# or Visual Basic code to use in your apps.
There is also a .NET Framework version of this sample available on Microsoft samples portal.
Pre-release version of this package is available from NuGet Gallery