Not to mention how it was basically a more restricted WPF (which already is an over-engineered, confusing mess)
From a design standpoint they have been working to merge their Fabric design system (started by the Office team and originally focused on web, then React, but now with a bunch of Fabric UI Native controls especially for React Native and Xamarin) with their UWP design work (Fluent Design System 2.0 and the WinUI controls library). That merger in progress is working to sell Fluent Design as a cross-platform design system that feels native on each platform (adapting to be more Material Design-like on Android, and more Apple-design like on iOS), but also coherent (and brandable) across platforms (since many users use multiple platforms each day).
It's an interesting strategy, and maybe even a great idea to have a cross-platform design system focusing particularly on stuff that matters (accessibility is huge focus area for Fluent Design), and with Office seemingly all in on this strategy it may even have weight to it. It's also something that potentially complements the Xamarin and React Native approach well, of adapting to native components and feel as much as possible, but trying to leverage as much high level similarity as possible as well.