Flatpak: When mouse outside grid cannot use keyboard to control grid cursor

[jeremypw]

When the mouse leaves the grid the headerbar gets focus and pressing Tab does not return the focus to the grid. Therefore in order to use the keyboard to operate the game, you have to place the mouse onto the grid.

It should not be necessary to operate the mouse in order to operate the game with the keyboard.

[jeremypw]

The Gtk4 version under development does not seem to have this problem - keyboard focus remains with the grid. All headerbar tools have keyboard shortcuts revealed in tooltips. May need to add a Shortcut Window as well?