Recently I was in game and invited to a group chat instead of having established the group chat prior to launching the game.

Both the notification for said chat only appeared within the game's window (Civ BE) and I was also unable to get the group chat window to open /outside/ of the game window space without first closing the game, establishing the group chat, and then launching the game.

All of those notifications should appear in both places. Aside from escaping the game with shift+tab I really don't use the in game overlay.