A Microsoft platform for building and publishing apps for Windows devices.
Thanks for the responses. We contacted Microsoft and they are willing to sell us a license to continue using Bing maps for another year.
It's too bad that we have to resort to using a web view but I guess that's what we'll do.
The idea of "migrating" to WinUI3 sounds great and is easy to say, but we're talking about a huge application that took years to develop, so it's an expensive undertaking.