The Brainpower overlay will be activated after Nightbot notices two uses of the keyword of your choice (usually o-oooooo or generator).
Make sure you are using the most up-to-date version of Multiplatform OBS Studio, and have CLR Browser plugin installed.
Set the Width and Height to match your stream resolution (1920x1080), make it fullscreen, and go for 60FPS
is Nightbot's default response when it sees the keyword in your chat. If you see (ditto), you should add it to your channel's emote list in Better Twitch TV. If you don't want (ditto) to be Nightbot's response, enter it here and get your updated nightbot command above.