Comment 4 for bug 1738283

By default virt-manager will *not* enable the '-k en-us' argument, because that forces use of a specific keyboard layout in QEMU's VNC server. For that to work, the VNC client keymap must exactly match the QEMU VNC server keymap, and must also exactly match the guest OS keymap.

Instead virt-manager leaves off the "-k en-us" argument, which will cause the VNC servers raw scancode extension to be activated with compatible clients. Virt-manager uses GTK-VNC which activates this extension, and so passes raw XT scancodes from virt-manager to QEMU to the guest OS, which generally makes everything "just work"

IOW, if virt-manager works correctly, but tigerVNC does not work correctly, this probably means that tigervnc is not activating the raw scancode extension.