Up front, I found this answer and it didn't help (read below).
I am using
vanilla-gnome-desktop in Ubuntu 18.04 and I have not been able to pass through special keys like Windows (aka Super) to the session connected in Remmina.
I have assigned that key (Super) to a number of global shortcuts in the GNOME shell for convenience (e.g. Super+T for Terminal and Super), though.
However, as I understand it Remmina should be able to do just that by activating a sort of "grab all keys" mode with Control_R (right Ctrl key). And indeed hitting that key toggles the respective icon in that floating bar Remmina provides when inside a connected session. However, it appears to have no effect whatsoever. The following screenshot illustrates the icon/button (and underlying setting) I mean:
For example hitting Alt+F4 simply closes the Remmina window, instead of closing whatever window I have focused inside the session. Hitting Super will open that quick launch thingamy (no idea what the proper term is) and not the start menu inside the session.
The keyboard settings for Remmina look as follows:
So what am I doing wrong here?
My goal is to have Remmina (and thus the connected session) receive the maximum number of special keys, although it's perfectly acceptable to have an "escape" like in virtualization GUIs.