One of the things I noticed was that some of the tool windows I was used to from UWP weren’t working as I expected. I recall hearing that Microsoft had been working on things like hot reload for WinUI, so I was surprised that I couldn’t edit XAML and for it to update in the running application.
It turns out that there’s a flag in the Options window (Tools menu, Options) in the Environment, Preview Features section entitled “Enable UI Debugging Tooling for WinUI 3 Projects”.
I’ve got no idea why this is off by default but if you turn it on you get almost instantaneous hot reload when you change your XAML (unless you do what I did which was to enter XAML that referenced a namespace that I hadn’t imported!).