Uno is a really interesting approach to writing cross-platform UIs. It's interesting that they basically have a native implementation of say Button for every platform.

This might lead to a unified style across platforms but as it does not use the same rendering logic/code on every platform I'd doubt that it's pixel perfect. Building a text editor would probably expose a lot of these close but not similar scenarios.

On the other hand this adds the benefit of getting native behaviour of text boxes maybe ?

Avalonia on the other hand does custom rendering using Skia and therefore really has pixel perfect rendering across platforms. This also means that it does not use the native controls and behaviour differs.

If I had to write a cross platform app (and had the budget) I would probably use Xamarin and just write platform specific UIs. If there are heavy UI components these could still be shared.

If on a budget something like this seems fine. Would probably go with avalonia UI tho tbh.