Hi,
Try to have the cinemachine brain be updated in Late Update. And you could also try to set the “Interpolate” value in the Rigidbody component of the player game object to “Interpolate”.
https://forum.unity.com/threads/stuttering-with-rigidbody-cinemachine.1141687/#post-7334470
Last but not least, if the issue persists, create a build and test it because the game window is just a (laggy) preview.
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