These days, I think Microsoft's web-based desktop apps mostly use WebView2 directly instead of Electron, so they don't have to bundle a browser. I think for Teams it happened at the same time that they moved from Angular to React.
The point about them not using MAUI still stands though. From what I understand, the .NET world has either adopted different abstractions like Avalonia, or stuck with tried and tested solutions like WinForms with proprietary controls. After all, they've seen this before with WPF which was never fully adopted by MS either, or with the debacle around Metro/WinRT. You're never quite sure what Microsoft wants you to use or will support in the long term. They also make Blazor, which is a different (and likely more accessible) way to build web apps with .NET.
Since we're on the subject of companies not dogfooding their shiny tech, is Google really using Flutter for their own apps? I feel like the evolution of the Android ecosystem towards Kotlin and Jetpack Compose implies otherwise.