How to rotate camera counterclockwise using quaternions and euler angles?

Question

Unity

The Q and E buttons are assigned to rotate the camera by 90 and -90 degrees.
The camera on the stage consists of a holder and a camera inside it; is rigidly attached to the character, follows his movement (as in diablo, titan quest, grim dawn, etc) and revolves around him.
Turning clockwise (+90 degrees) works correctly and turns smoothly, but when I turn it counterclockwise (-90 degrees): the camera starts to jerk, or turns too sharply.

void Turning(){
    Quaternion quatertion = transform.rotation;
    Vector3 eulerAngle = new Vector3(0, quatertion.eulerAngles.y, 0);
    
    if(rotationAngle - eulerAngle.y < 0.2f){
      if(rotationAngle == 360){
                rotationAngle = 0;
      }
            eulerAngle.y = rotationAngle;
            isTurning = false;
    } else {
      eulerAngle.y = Mathf.Lerp(eulerAngle.y, rotationAngle, rotationStep * Time.deltaTime);
    }
    m_Compas.rotation = eulerAngle.y;
        quatertion.eulerAngles = eulerAngle;
    parentTran.rotation = quatertion;
  }

How to improve this code?
Upd.1:
Chthonic hulk that doesn't work

void Rotator(float val) {
        rotationAngle += val;
        Quaternion quatertion = transform.rotation;
        Vector3 eulerAngle = new Vector3(0, quatertion.eulerAngles.y, 0);
        if (rotationAngle > 0) {
            if (rotationAngle - eulerAngle.y < 0.2f) {
                if (rotationAngle == 360 || rotationAngle == -360) {
                    rotationAngle = 0;
                }
                eulerAngle.y = rotationAngle;
                isTurning = false;
            } else {
                eulerAngle.y = Mathf.Lerp(eulerAngle.y, rotationAngle, rotationStep * Time.deltaTime);
            }
        }
        else if (rotationAngle < 0) {
            rotationAngle = 360 + rotationAngle;
            if (rotationAngle - eulerAngle.y < 0.2f) {
                if (rotationAngle == 360 || rotationAngle == -360) {
                    rotationAngle = 0;
                }
                eulerAngle.y = rotationAngle;
                isTurning = false;
            } else {
                eulerAngle.y = Mathf.Lerp(Mathf.Abs(rotationAngle), eulerAngle.y, -rotationStep * Time.deltaTime);
            }
        }
        m_Compas.rotation = eulerAngle.y;
        quatertion.eulerAngles = eulerAngle;
        parentTran.rotation = quatertion;
    }

Current Solution:

void Camera_Rotation() {
        if (rotationAngle > 0) {
            transform.RotateAround(targetGO.transform.position, Vector3.up, -rotationAmount);
            rotationAngle -= rotationAmount;
        }
        if (rotationAngle < 0) {
            transform.RotateAround(targetGO.transform.position, Vector3.up, rotationAmount);
            rotationAngle += rotationAmount;
        }
    }

Answer 1

Quaternion neededRotation = transform.rotation;
neededRotation *= Quaternion.Euler(0, 90, 0); // this add a 90 degrees Y rotation
transform.rotation = Quaternion.Slerp(transform.rotation, neededRotation , Time.deltaTime * damping);
I wrote very fast, so just the general meaning:
Remember the current turn.
Add the one you want to it.
And gradually, as you like, from the current to the desired one, at least immediately, at least through Lerp, rotate.
I hope it helps)