Would it be possible to add Lft Ctrl + WinKey as "System Key Shortcut"? Reason being that if I press the sys key then I can do things like Alt+Tab on my local machine. But as I prefer to use left hand shortcuts, the only options I have are Left Ctrl or Left Alt, which means I can't do things like Ctrl + V and Alt + F4 on the remote session.

Multi-hostkey shortcuts and Windows Key in particular are a can of worms that caused a lot of issues. There's a difficulty managing what is exposed to the application when the underlying RD control has focus. I'm toying with the idea of changing the way it's done entirely, so instead of shortcut keys, it's just an "escape" key that breaks you out of focus, then all the normal shortcuts work.

It's kind of far down my priority list right now. Sorry!