1) Buy a basic HTML template online for your app's dashboard.
2) Don't use Electon. Your users WILL notice and complain about performance. Instead, use the native WebBrowser control in .NET for Windows and WebView using macOS to display your UI. Disable right clicking and highlighting using HTML/JS. To the user, it'll feel like any other native app. Add this meta tag to the HTML file to ensure the WebBrowser control knows to use new versions of IE to render the UI: <meta http-equiv="x-ua-compatible" content="ie=edge"> (and/or look up how to add the FEATURE_BROWSER_EMULATION registry key)
3) Use the built in script calling functions to transfer settings back and forth between the UI and main app in JSON. Do the back end stuff in native code.
4) You can then re-use most of the UI code you wrote to easily port over to macOS. Use the same functions and logic you wrote on Windows to make your Swift functions.
* I've been making a living from building/maintaining my desktop application for about 5 years and had no regrets setting it up this way. I've also seen a number of other expensive, high-end, "professional" software using the FEATURE_BROWSER_EMULATION registry key trick.
Good luck!