I’ve just used the Project Template to create a new plugin, and I had to add the -windows to the TargetFrameworks element, since I’m using WPF/WinForms.
Upon starting Debugging from Visual Studio no breakpoints can be hit, even though the plugin is loaded.
You’re likely not hitting breakpoints because Rhino is still configured to use .NET Framework. You need to ensure you run Rhino.exe in .NET Core mode. You can usually add /netcore as an argument to Rhino.exe in your launch configuration to force that mode even if you’ve configured Rhino to run in .NET Framework when run directly.