This repo contains a solution with a WinUI 3 app and a Blazor WASM app. The solution shows how a WinUI app can communicate with a hosted Blazor App via JavaScript interop.
Read more about this solution in these two blog posts:
https://www.thomasclaudiushuber.com/2020/02/19/calling-winui-from-blazor-app-hosted-in-webview2/