Yes. This is related to the EOL of Silverlight ( https://learn.microsoft.com/en-us/previous-versions/windows/silverlight/dotnet-windows-silverlight/cc197955(v=vs.95) ). Please move your app to either the V8 Web control or UWP Maps control. The Silverlight Maps control was deprecated in 2016 as documented here: https://www.microsoft.com/en-us/maps/discontinued-control-migration-guidelines
If you must rely on crossdomain, you can host your own server as a pass through and have that server call the API, but I believe this will only be a temporary fix and moving to a modern control is the right answer. We have a demo of how to use your own server to deploy your key https://greymatter.com/content-hub/protecting-and-hiding-your-bing-maps-key/ that can be extended to have the cross domain xml as well.