This was the first post I found on this topic, so leaving this hint here for others with the same question: It is possible with no extra code by using a composite binding in the “Look” input action that by default drives the Look Orbit X and Y axis in the Cinemachine Input Axis Controller.
Replace the “Delta pointer” binding with a one-modifier composite binding that requires the mouse button to be held for the Delta pointer binding to come through.
See also Input System documentation one composite bindings: Input Bindings | Input System | 1.8.2