[neonsunset]

Interestingly enough, in practice, there are various declarative SwiftUI-style nuget packages for Avalonia[0][1][2] and Uno[3]. You don't actually have to touch XML if you don't want to.

Edit: as someone else noted, the website itself links to a built-in option to do so as well - https://platform.uno/c-markup/

[0] https://github.com/AvaloniaUI/Avalonia.Markup.Declarative

[1] https://github.com/wieslawsoltes/NXUI

[2] (F#) https://github.com/fsprojects/Avalonia.FuncUI

[3] https://github.com/VincentH-Net/CSharpForMarkup