DeltaTime fluctuation has been an issue in Unity for some time. You can read all the gory details here: Time.deltaTime Not Constant: VSync CameraFollow and Jitter
The good news is that this is being fixed, and DeltaTime will be much more steady in the near future (it’s a non-trivial fix, but it is happening).
The bad news is that camera damping is one of those things that’s very sensitive to a fluctuating deltaTime. Most of the jitter is specific to the Unity Editor, and is substantially reduced in the build (it is in your project). Often, this reduction (though not perfect) is good enough. If it isn’t, then the only workaround for the time being is to turn off damping, or use RigidBodies without interpolation and set the CM Brain to FixedUpdate. Then the cameras are rock-steady.