It seems that you are using .NET 8, not .NET Framework.
To use the charts, try to close the Form Designer, right-click the WinFormApp7 project in Solution Explorer, select “Manage NuGet packages”, go to Browse tab, find the “WinForms.DataVisualization” package and install it. Reopen the form and find the chart control in Toolbox.
The charts should be also available if you create a new “Windows Forms App (.NET Framework)” project instead of “Windows Forms App”.