Improve the XAML UI render performance
The UI render performace is not good, despite of you follow the XAML optimization guides there is scenarios where you have to render a big visual tree, for example more than 8000 items, and in this cases the UI freezes when is loading the visual tree. The UI freezing is the major issue I see in UWP and seems to not be improving, and I'm working with this platform from the first day.
Also, can you post this on the WinUI repo (https://github.com/microsoft/microsoft-ui-xaml)? That's where the XAML team is tracking open issues and putting all new feature work.
It would be useful to understand the kinds of UI and scenarios you're dealing with that require 8,000 items on load. Perhaps there's a list of repeated content that isn't virtualizing correctly?
I agree that the load delay is something that should be worked on somehow. But if you have 8000 items on screen, then you have done something wrong, definitely. This is not something that an automatic layout system can handle.