Camera passing through terrain. Please help

I found another solution for anyone needing. Previously I had suggested putting Rigidbody and Sphere Collider to Camera (Collider has Trigger, Rigidbody is without gravity, freeze rotation X and Z from the constraints too) But still the camera enters to terrain if player insists to go down the terrain and it clips the terrain (I changed terrain thickness to great numbers, still "sometimes" camera was entering into terrain.

So I developed another solution on the below, this minimizes passing through terrain very much.

Notes: The bottom part is your Mouse Scroll code, and the rest of the script is to limit the camera going below Terrain. I left comments above each section. Please make sure to add Sphere Collider (with Trigger on) and Rigidbody as I mentioned on the above message of mine. Then apply the script below.

Also I considered the Terrain has "Terrain" tag, change it if you use something else, but make sure your Terrain has a tag.

     [Tooltip("The time to move Cam away from Terrain")]
     public float smoothTime = 0.1f; //Make it 0.1f, 0.3f, 1f or any number according to your preference. This defines movement speed of cam if cam collides with terrain. Smaller number means quicker movement.  
     [Tooltip("The min permitted Height limit between Cam and Terrain")]
     public float minCamTerrainHeight = 0.15f;
     [Tooltip("Raycast height from the Cam to Terrain")]
     public float terrainDetectionHeight = 2f;
     public float zoomSpeed = 350f;
     private Vector3 velocity = Vector3.zero; 
     private bool colliding = false;

 void  OnTriggerEnter (Collider other){ 
     if (other.gameObject.CompareTag("Terrain"))
         colliding = true; 
 }

 void  OnTriggerExit (Collider other){ 
     if (other.gameObject.CompareTag("Terrain"))
         colliding = false; 
 }
 
         //If Camera collides with Terrain, move the camera smoothly above the terrain
         if (colliding){ 
             transform.localPosition = Vector3.SmoothDamp(transform.localPosition, new Vector3(0,minCamTerrainHeight,0), ref velocity, smoothTime); 
         }
 
         //Check Distance between Terrain-Camera object
         RaycastHit hit;
         if(Physics.Raycast(transform.position, -transform.up, out hit, terrainDetectionHeight)) {
             //If the camera is at a certain height above the Terrain, limit Mousescroll going down further but don't limit it going up:
             if(hit.collider.tag=="Terrain"){  
                 print("Camera is very close to Terrain.");
                 float moveDown = Input.GetAxis("Mouse ScrollWheel");
                 if (moveDown < 0)
                     transform.Translate(new Vector3(0, moveDown) * Time.deltaTime * -zoomSpeed, 0);
             }
         }
         else
             //move the camera when you scroll. This happens if it is above the terrainDetectionHeight.
             transform.Translate(new Vector3(0, Input.GetAxis("Mouse ScrollWheel")) * Time.deltaTime * -zoomSpeed, 0);

Here is a basic camera follow script for

1. Smooth zoom

2. Ground detection moving closer to the player until the raycast is above the ground.

      // Main
        public bool cameraEnabled = false;
        public float cameraTargetHeight = 1.5f;
        public float mouseSensitivity = 3f;
        public float lerpSpeed = 15f;
   
        // Zoom
        public float zoomSensitivity = 5;
        public float zoomStartDistance = 2;
        public float zoomMin = 1.5f;
        public float zoomMax = 20;
   
        // Ground Collision
        public float maxCollisionDetectionDistance = 0.5f;
        public float collisionCorrectionIncrement = 0.2f;
    
        private float x = 0.0f;
        private float y = 0.0f;
        private float distance = 3.0f;
        private float currentDistance = 3.0f;
   
        void Start()
       {
           distance = zoomStartDistance;
           currentDistance = zoomStartDistance;
       }
   
           void LateUpdate()
            {
                if (!cameraEnabled)
                    return;
        
                if (Input.GetMouseButton(1))
                {
                    x += Input.GetAxis("Mouse X") * mouseSensitivity;
                    y -= Input.GetAxis("Mouse Y") * mouseSensitivity;
                }
        
        
                    float targetRotationAngle = cameraTarget.eulerAngles.y + rotateTargetOffsetY;
                    float cameraRotationAngle = transform.eulerAngles.y;
        
                    x = Mathf.LerpAngle(cameraRotationAngle, targetRotationAngle, lerpSpeed * Time.deltaTime);
                }
        
                y = ClampAngle(y, -50, 50);
        
                Quaternion rotation = Quaternion.Euler(y, x, 0);
        
                // Extremely basic collision where the current distance is reduced until the camera is above the ground
                RaycastHit hit;
                if (Physics.Raycast(transform.position, -transform.up, out hit, maxCollisionDetectionDistance ))
                {
                    currentDistance -= collisionCorrectionIncrement;
                }
        
                // Smooth zoom
                currentDistance -= Input.GetAxis("Mouse ScrollWheel") * zoomSensitivity;
                currentDistance = Mathf.Clamp(currentDistance, zoomMin, zoomMax);
                distance = Mathf.Lerp(distance, currentDistance, Time.deltaTime * zoomSmooth);
        
                Vector3 position = cameraTarget.position - (rotation * Vector3.forward * distance + new Vector3(0, -cameraTargetHeight, 0));
        
                transform.position = position;
                transform.rotation = rotation;
            }
        
            private float ClampAngle(float angle, float min, float max)
            {
                if (angle < -360)
                {
                    angle += 360;
                }
                if (angle > 360)
                {
                    angle -= 360;
                }
                return Mathf.Clamp(angle, min, max);
            }