RenderTexture causes memory problems

Hi, I have the following code placed in a GUI Window function. I use this to save a RenderTexture rendered by a camera in the "finalRT" variable.

     public RenderTexture finalRT;
     
     void NodeWindow(int windowID)
     {
         RenderTexture heightmapRT = RenderTexture.GetTemporary(1024, 1024, 24, RenderTextureFormat.ARGB32);
     
         GameObject renderCamera = new GameObject();
         renderCamera.AddComponent<Camera>();
         renderCamera.GetComponent<Camera>().backgroundColor = Color.black;
         renderCamera.GetComponent<Camera>().orthographic = true;
         renderCamera.GetComponent<Camera>().orthographicSize = 5;
         renderCamera.GetComponent<Camera>().transform.localPosition = new Vector3(9999, 10009, 9999);
         renderCamera.GetComponent<Camera>().transform.localRotation = Quaternion.Euler(new Vector3(90.0f, 0.0f, 0.0f));
     
         GameObject renderPlane = GameObject.CreatePrimitive(UnityEngine.PrimitiveType.Plane);
         renderPlane.transform.localPosition = new Vector3(9999, 9999, 9999);
         renderPlane.transform.localRotation = Quaternion.Euler(new Vector3(0, 0, 0));
         renderPlane.GetComponent<MeshRenderer>().sharedMaterial.shader = GetNodeByOutput(finalInput.matchedOutput).material.shader;
         renderPlane.GetComponent<MeshRenderer>().sharedMaterial.CopyPropertiesFromMaterial(GetNodeByOutput(finalInput.matchedOutput).material);
     
         renderCamera.GetComponent<Camera>().targetTexture = heightmapRT;
         renderCamera.GetComponent<Camera>().Render();
         RenderTexture.active = heightmapRT;
                 
         finalRT = heightmapRT;
                 
         renderCamera.GetComponent<Camera>().targetTexture = null;
         RenderTexture.active = null;
         DestroyImmediate(renderPlane);
         DestroyImmediate(renderCamera);
         RenderTexture.ReleaseTemporary(heightmapRT);
     }

The code works and I'm satisfied with the result, but the system memory is constantly going up. I thought I deleted everything generated at the beginning (renderTexture, camera, plane) so I don't understand. If I remove the clean-up code at the end, memory sky-rockets and causes a crash in seconds, so the clean-up does something. It's just not enough (RAM usage goes up 400K/s).

Does anyone have an idea what the problem would be?

Thanks.