You are looking at XAML, which underlines WPF, Silverlight, UWP/WinUI as the layout description language.

You can also do it in pure .NET code without XML, hence why I specifically mentioned code first.

So to pick on your example,

    var btn = new Button
    {
        Name = "Button",
        Content = "Hello, world!",
        HorizontalAlignment = HorizontalAlignment.Left,
    };
    btn.Click += (s, e) =>
    {
       // handle click event
    };

Slightly more verbose, but one can still wrap those calls, or just pick Fabulous, https://github.com/fsprojects/Fabulous

WinUI is the latest tech, just UWP as usual, still the future of Windows UI, now re-architected not to depend on a specific Windows 10 release, going back all the way to Falls Creator.