Comment 2 for bug 1726910

Adding a toolbar with function keys consumes alot of screen real estate for something that is going to be rarely used in practice.

The more usual approach to this problem is for the application to grab the keyboard and block all local window system accelerators, so that Fn goes straight to the guest OS when the console window has focus. This is done by GNOME Boxes, virt-viewer, virt-manager, and I though QEMU's frontends did it by default too.

Recently though, there has been a regression in this area. With the switch to Wayland instead of Xorg, the standard GTK APIs for doing this keyboard grabbing / accel blocking no longer work correctly. Instead apps need to add custom code to talk to the Wayland compositor IIRC. There's work underway to address this but its a way off.

Some key combinations are hard to deal with, even with the above approach. For that reason virt-viewer/virt-manager, etc typically have a "Send key" menu item, populated with a set of special sequences. Typically this covers Ctrl+Alt+fn sequences, and Ctrl+Alt+Delete and a couple more.