Cannot build UWP project: Missing 'Windows' namespaces

Problem

Building a UWP project in Rider results in errors such as:

Error CS0234: The type or namespace name 'ApplicationModel' does not exist in the namespace 'Windows' (are you missing an assembly reference?)
Error CS0246: The type or namespace name 'Application' could not be found (are you missing a using directive or an assembly reference?)

Cause

These errors commonly occur if the Universal Windows Platform (UWP) SDK or required tooling is not installed or correctly configured.

Resolution

Install the prerequisites of UWP via either of the following:

1. Run Visual Studio installer

2. Install "WinUI application development" workload:

   

3. Download and install Windows SDK.

References

Setup for WinUI - Windows apps (Microsoft Documentation)