While there is a code sample that lets us define a BoolToObjectConverter like so:
<converters:BoolToObjectConverter x:Key="BoolToVisibilityConverter" TrueValue="Visible" FalseValue="Collapsed"/>
It is not among the available options when using the Microsoft.Toolkit.Uwp.UI.Converters namespace in a third-party UWP app (see attached image).

BoolToObjectConverter is a public class; why doesn't it appear in this list?
Are you using the project code in your solution? Or the nuget package? If the latter, then it won't be in that until the next update for it.
@ScottIsAFool Thanks, this is noted. I'm using the NuGet package. Does this need to stay open until the next release?
Probably not. The code sample is only on the dev branch, which means it hasn't been pushed to master (and so the nuget package). If you update the nuget package when that update goes out and you still don't have the converter then, then re-open this issue.
Pre-release packages are available for our dev repo: https://ci.appveyor.com/nuget/uwpcommunitytoolkit-unwg9jaovwyr