One of my favorite XAML Control primitives is the Panel class. It's what drives Grid, StackPanel, Canvas and many many other controls that contains a set of other controls, and controls layout the children out in the view.
So in my second twitch stream, I walked through creating a custom panel that lays out controls in a grid-like manner, without having to do all the row and column definitions. It mainly focuses on the Arrange and Measure steps in the layout life-cycle, which applies to both WPF, UWP and WinUI (or even Silverlight for that matter ;-). And just for fun I used the latest WinUI 3.0 Alpha release (but it really doesn't matter as the concepts are the exact same - only namespaces differs).
And please subscribe to my YouTube and Twitch channels!