Просто это что-то типа maui ?Avalonia UI is an open source framework for building stunning, desktop, mobile, web and embedded applications using a .NET single codebase.
Крч на реддите сам же ответ нашел MAUI is an evolution of Xamarin Forms. Marketing will call it "cross-platform" or "write-once run-anywhere". What it is is a cross-platform mobile framework that can run on desktop.
Avalonia is a recreation of WPF. It is a cross-platform desktop framework that is trying to add features that let it run on mobile.
Windows vs. Mac vs. Linux is a small potatoes comparison. These are all desktop environments and Avalonia does a good job of representing that paradigm across them all. Android vs. iOS is a small potatoes comparison. Xamarin Forms and several other frameworks do a good job of representing the mobile paradigm on both platforms.
"Desktop" vs. "mobile" is a big consideration when writing an app. I think they are so different, no framework that claims to support both does so in a satisfying way. Some people think it's impossible, I'm not convinced of that yet but I do believe using any framework that tries to blend them will inevitably make compromises.
So I don't think Avalonia vs. MAUI is a fair comparison. Avalonia is going to represent a desktop paradigm very well because that's what it was designed for. MAUI has to represent the mobile paradigm, and while it works on Windows and Mac any app you make will feel like "a mobile app running in an emulator" more than it will feel like a native desktop app.
For some apps that doesn't matter. Discord, Slack, and a ton of art apps work just fine in a mobile paradigm. For things that heavily use the mouse and keyboard (like Office) or multiple windows (like many engineering apps) you have to go about them different ways on mobile and desktop.
MAUI doesn't and can't do a great job at that because its general approach is to present the biggest common subset of features on its platforms. It can't really focus on Desktop because that would make its usability for mobile worse. MAUI's real use case is for places that have a C# team, want to make a mobile app, and don't think they can afford to hire dedicated iOS and Android developers. It lets you use a XAML framework to write a mobile app and it's pretty decent at that. It is true that MAUI itself is immature, and the toolset is janky, and there's not a lot of confidence in it, but it's still important to understand many people are trying to use it for a use case it cannot serve.
If you want a Windows-only desktop app you should use WPF. If you want cross-platform desktop apps AvaloniaUI is more appropriate, and some people prefer just starting with it. If you are more interested in mobile apps, MAUI is appropriate and you may find the desktop experience adequate.
But don't get me wrong, while MAUI is not great as a "run anywhere" framework, there really aren't ANY great "run anywhere" frameworks. They all focus the most on either mobile or desktop and present a compromised feature set for the other