Hi,
Never done it, but I think theses potential solution. I would ask on Unity forum as well.
- create two cinemachine camera, one that rotates with the player and one that doesn't, then you switch from one to the other when you press that button, once the camera has rottated behind the player you can switch back.
- control the camera rotation directly yourself, using playmaker, have you tried that?
Bye,
Jean