Keys can't be grabbed under Wayland (needed by remote desktop viewers, virtual machine managers).
Comment 33: With X11 clients, there is a (preconfigured, but changable) white list of clients whos grabs will be granted allowing them to work as intended. See org.gnome.mutter gsettings
Where is this white list?
Asked: Who manages this list and how do we (xpra) get in on it?
Found the magic key in mutter and made a pull request: add 'xpra' to the list of xwayland clients that can do grabs
No reply so far..
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2613