Basically XAML/WPF/UWP code first.

Which one is their latest tech? Where does "WinUI" fit in? Is there a good, single starting point like SwiftUI's tutorial?

The first hit brought me to "Host a custom UWP control in a WPF app using XAML Islands" so there seems to be a distinction (and it implies WPF isn't the star anymore?)

[0] [1] that I could find after a couple searches look way more complex than what the equivalent SwiftUI would be.

    <Button x:Name="button" Content="Hello, world!" HorizontalAlignment="Left" Margin = "152,293,0,0" VerticalAlignment="Top"/>

vs.

    Button(action: play) {
        Text("Hello, world!") // Don't need alignment etc. to produce identical output.
    }

and ugh [2]:

> If you need to embed any Unicode characters into the text, you can use the standard XML syntax. For example, to put the greeting in smart quotes, use: <Label Text="&#x201C;Hello, XAML!&#x201D;" />

I suggested emulating SwiftUI's syntax because it seems to be the most succinct.

[0] https://github.com/microsoft/Windows-appsample-photo-lab/blo...

[1] https://docs.microsoft.com/en-us/windows/uwp/get-started/cre...

[2] https://docs.microsoft.com/en-us/xamarin/xamarin-forms/xaml/...

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.

Thanks. Couldn't find a "code first" example before my irrational impatience with Microsoft kicked in :P

I haven't touched C# in ages but that definitely looks odd compared to what I remember of it (like SwiftUI looks a little odd compared to Swift but not by this much.) My immediate thought: why capitalize the property names?

Fabulous is comparatively verbose too but probably more idiomatic with F# (which I have no experience with.)