Hi Sigma,
I agree with Viorel, please install “.NET desktop development” workload from VS Installer (Visual Studio Installer > find VS 2019 > More > Modify > select the workload > Modify).
Besides, I noticed that you just installed Universal Windows Platform development in VS, so did you create a UWP (Universal Windows Platform) project, and right-clicked the project to try to add a Window (WPF)? If yes, I’m afraid, you can’t add a Window(WPF) in a UWP project, please create a new WPF project after installing the “.NET desktop development” workload, and try to add a Window (WPF) in WPF project.
Best Regards,
Tianyu