I understand the need for some apps to work on desktops, but I haven't personally done any of these before. Just iOS and Android, is all clients ever seem to ask me. So of course Flutter wouldn't work well for desktop atm. But FYI: it is being looked at - https://github.com/google/flutter-desktop-embedding Even seen an MS employee contributing to it as well.

As for Dart, its similar to C# in a lot of ways and certainly is gaining traction. I didn't have any difficulty writing Dart code.