If you have something to say, better post it here, for now
It's middle mouse button by default. Probably it's confusing, that middle mouse button is called mouse2 in settings menu, but this is just how it's called internally.
There is rotate feature for the camera, camera rotated by mouse when you use 2nd control scheme (free camera). Use left ctrl to toggle it, this way you can use mouse to rotate the camera instead of steering, and steer using keyboard. These controls i got used to play in another game, so i just made very similar ones in my own. If you want to press and hold a named button to rotate the camera, then yes, there is no such feature, i will add it in the next update, together with button remapping, thx for suggestion.
I will be busy in the beginning of the month, so expect fixes in late october.