SIGN-IN PROCESS IN DROPBOX-SDK-DOTNET

I tried SimpleTest and OAuthPKCE in the dropbox-sdk-dotnet package.
They work fine, however after the sign-in process, and even after the program has ended, the computer browser (Microsoft Edge) remains open on page 127.0.0.1. How can I programmatically close and dismiss it?
I also migrated the same test program in Xamarin - here the instruction System.Diagnostics.Process.Start(authorizeUri.ToString()); throws an exception and I replaced it with: await Xamarin.Essentials.Browser.OpenAsync(authorizeUri); But I have the same issues: the browser page remains open on page 127.0.0.1 after the sign-in process.