Specify Both X And Y

The [ObservableObject], [ObservableProperty] and [ICommand] attributes come from the CommunityToolkit.Mvvm package, you can read more about it here.

This web site wraps every sample using a UserControl instance, but LiveCharts controls can be used inside any container.

sample image

View model

using CommunityToolkit.Mvvm.ComponentModel;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.SkiaSharpView;

namespace ViewModelsSamples.Lines.XY;

public partial class ViewModel : ObservableObject
{
    public ISeries[] Series { get; set; } =
    {
        new LineSeries<ObservablePoint>
        {
            Values = new ObservablePoint[]
            {
                new ObservablePoint(0, 4),
                new ObservablePoint(1, 3),
                new ObservablePoint(3, 8),
                new ObservablePoint(18, 6),
                new ObservablePoint(20, 12)
            }
        }
    };
}

XAML

<UserControl x:Class="AvaloniaSample.Lines.XY.View"
             xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:lvc="using:LiveChartsCore.SkiaSharpView.Avalonia"
             xmlns:vms="using:ViewModelsSamples.Lines.XY">
  <UserControl.DataContext>
    <vms:ViewModel/>
  </UserControl.DataContext>
  <lvc:CartesianChart Series="{Binding Series}"/>
</UserControl>

Articles you might also find useful:

Cartesian chart control
Line series properties