Stawsh I don't honestly have an answer to that. I can tell you that the staple Office 365 software products all have webcode in them. It's in Excel and Word for certain. But they are component elements of the desktop application and not the foundational codebase, which is the case for New Outlook. If you look closely at Word when it renders elements of the document or syncs with OneDrive to tell you "where you left off, ". And certain elements of Excel and how it renders UI components of the software.
But can I say that MSFT will come along and take Word Online and Excel Online and box them up in a React Native wrapper and render the user interactive elements with WebView2, just as they have done with New Outlook, New Teams, and other applications? I don't think that would come for a while. But the more they want to push Microsoft Copilot into their products, the more you are going to see web code. For some reason, it seems to be that the AI components require web code to be injected into the product. It might have to do with their AI's software's reliance on web connectivity for it's functionality.
And there are web code elements of Windows itself. The settings menu for example is heavily web based. It seems to be difficult for Microsoft to develop desktop applications in native code anymore. They may not even have a full team there who can build applications in C anymore outside of the group that develops Windows.