gistfile1.cs

IEnumerator Shake() {
        
    float elapsed = 0.0f;
    
    Vector3 originalCamPos = Camera.main.transform.position;
    
    while (elapsed < duration) {
        
        elapsed += Time.deltaTime;          
        
        float percentComplete = elapsed / duration;         
        float damper = 1.0f - Mathf.Clamp(4.0f * percentComplete - 3.0f, 0.0f, 1.0f);
        
        // map value to [-1, 1]
        float x = Random.value * 2.0f - 1.0f;
        float y = Random.value * 2.0f - 1.0f;
        x *= magnitude * damper;
        y *= magnitude * damper;
        
        Camera.main.transform.position = new Vector3(x, y, originalCamPos.z);
            
        yield return null;
    }
    
    Camera.main.transform.position = originalCamPos;
}

should position be calculated like this?
... = new Vector3(x + originalCamPos.x, y + originalCamPos.y, originalCamPos.z); // line 20

yes it should. this trivial example just has the camera at the origin which allows me to simplify a bit. However, if the camera was positioned somewhere else, you'd need to account for that like you suggest.