Pick a game and click Turn chat on. The dot goes green.
Click Show Slot Tools command and paste it as the Response of a Slot Tools command named play, Permission Everyone. It holds your private key: keep it off stream.
Keep this page open (a browser tab, or an OBS browser source pointed at this page). Viewers type !play. Page closed = the command stays quiet.
One command works for every game: switching games here needs no Slot Tools change.