Notifications never take keyboard focus on their own, since a card that grabbed focus as it arrived would swallow whatever you were typing. A keybinding hands the keyboard over: Super + Ctrl + comma, merged into quattro, selects the newest card, opens its deck, and gives that display's notification surface exclusive keyboard focus.

The keys 1 through 9 press a button, Enter clicks the card, and Escape gives the keyboard back, as does any choice, a mouse click on a card, the pointer moving onto another deck, or ten idle seconds. Silencing moves to Super + Ctrl + Alt + comma.