As the subject states, with the advent of component libraries in XD, I can no longer "Edit Main in Source Document".
Doing so will begin the process of opening the source document. However, once the opening progress bar reaches the end (presumably completion), the interface locks and the only way to close the window is to end task in Task Manager.
OS - Windows 10 Pro (Build 19041.572)
XD - "Up to date" no known way to determine build info