A couple other Shift modifier issues.
File - Open on windows brings up the file dialog box in many applications, eg, Notepad.
Within that dialog box, Tab moves you from input box to input box, whereas Shift+Tab moves your backwards through those same input boxes.
Tab works fine in Mac Viewer.
Shift+Tab however doesn't do anything that I can detect when using Mac Viewer logged into a Windows 10 host.
Similarly, Alt+Tab on Windows cycles through applications in the "Task Switcher" or "App Switcher".
Similarly, Shift+Alt+Tab is supposed to cycle through those apps backwards.
When using Mac Viewer on a Windows 10 host Opt+Tab does bring up the task switcher and cycle through apps. However Shift+Opt+Tab does nothing as far as I can tell.
Till the Mac Viewer is very usable and I'm getting a lot of work done with it.