Render depth to RenderTexture and calculate world position

Ok you can make a script that creates a copy of your desired camera, and renders with a replacement shader This particular script is attached to the camera, else you would need to get the camera by other means, here it can be accessed directly.

 public class Testing : MonoBehaviour {
 
     public Texture2D someTex;
     public RenderTexture myDepth;
     GameObject tempCam;
 
     void Start()
     {
         someTex = new Texture2D(Screen.width, Screen.height);
         myDepth = new RenderTexture(Screen.width,Screen.height,8);
         tempCam = new GameObject("tempCam");
         tempCam.AddComponent<Camera>();
         tempCam.camera.CopyFrom(camera);
         tempCam.camera.enabled = false;
     }
 
     void Update()
     {
         tempCam.camera.SetReplacementShader(Shader.Find("Custom/ReplacementShader"), "");
         tempCam.camera.targetTexture = myDepth;
         tempCam.camera.Render();
 
         RenderTexture.active = myDepth;
         someTex.ReadPixels(new Rect(0, 0, Screen.width, Screen.height), 0, 0);
         someTex.Apply();
     }
 }
 

Somthing like that, Leaving the replacement tag renders everything with the replacement shader.

A very simple shader to render depth can be as simple as forwarding your position down from the vertex shader into the fragment shader via TEXCOORD. and the color is the z value of the position divided by the far plane value of the camera which you pass in with the script.

 Shader "Custom/ReplacementShader" {
 
     SubShader {
         Tags { "RenderType"="Opaque" }
         
 
         CGINCLUDE
 
         struct VIN {
             float4 pos : POSITION0;
         };
 
         struct V2F {
             float4 pos  : POSITION0;
             float4 p    :TEXCOORD0;
         };
 
         V2F myVert( VIN i ) {
             V2F o;
             o.pos = mul( UNITY_MATRIX_MVP, i.pos );
             o.p = mul( UNITY_MATRIX_MVP , i.pos );
             return o;
         }
 
         fixed4 myFrag(V2F i) : COLOR {
             // Here my farplane is 10, hardcoded, you can pass it like any other parameter from the unity script.
             return fixed4(i.p.z / 10 , i.p.z / 10 , i.p.z / 10 ,1);
         } 
 
         ENDCG
 
         pass {
             CGPROGRAM
             #pragma fragment myFrag
             #pragma vertex myVert
             #pragma fragmentoption ARB_precision_hint_fastest
             #pragma target 2.0
             ENDCG
         }
     } 
 }

Then you should be able to use your imagination to use the data, and or optimize this code somehow to your liking.

Hope this helps somehow.