It's a SimHub widget overlaid over the game in OBS (as is the pedal widget and the paddle shifter indicators). You can easily use it on some kind of external screen (I have it on my phone dashboard), in a window on another monitor or on some other dedicated screen, or you can even use SimHub as an overlay over the game basically in the same way like it is in the video, except you have to run the game windowed or in borderless window for that to work, which might add some microstutter and is almost certain to add a bit of input lag (whether you mind or not is very subjective).
I don't rememeber if the widget is now standard part of SimHub install, or if it has to be installed separately (should be available here in the rF2 mods section somewhere I believe).