If we try to code a WPF App and I invite my friend to the LiveShare Session, he can only see the XAML Code, but not the Designer. Everything else works fine. Everything else with the LiveShare is fine. Why is the designer not viewable by my guest/friend?
Based off of this official page, App Sharing for WPF is not supported (as well as some other "winform"/desktop like platforms).
I also found a Visual Studio Feedback item that claims it's a known issue, but I suspect what they really meant is it's not supported:
This is a known issue for us and we plan to resolve it in the near future
Seeing that the post is fairly old, I don't expect Microsoft to make this a priority anytime soon.