Instanced rendering example from https://docs.unity3d.com/ScriptReference/Graphics.DrawMeshInstancedIndirect.html

InstancedExample.cs

using UnityEngine;
using System.Collections;

public class InstancedExample : MonoBehaviour 
{
    public int instanceCount = 1000;
    public Mesh instanceMesh;
    public Material instanceMaterial;
    public int subMeshIndex = 0;

    private int cachedInstanceCount = -1;
    private int cachedSubMeshIndex = -1;
    private ComputeBuffer positionBuffer;
    private ComputeBuffer argsBuffer;
    private uint[] args = new uint[5] { 0, 0, 0, 0, 0 };

    void Start() 
    {
        argsBuffer = new ComputeBuffer(1, args.Length * sizeof(uint), ComputeBufferType.IndirectArguments);
        UpdateBuffers();
    }

    void Update() 
    {
        // Update starting position buffer
        if (cachedInstanceCount != instanceCount || cachedSubMeshIndex != subMeshIndex)
        { 
            UpdateBuffers();
        }

        // Pad input
        if (Input.GetAxisRaw("Horizontal") != 0.0f)
        { 
            instanceCount = (int)Mathf.Clamp(instanceCount + Input.GetAxis("Horizontal") * 40000, 1.0f, 5000000.0f);
        }

        // Render
        Graphics.DrawMeshInstancedIndirect(instanceMesh, subMeshIndex, instanceMaterial, new Bounds(Vector3.zero, new Vector3(100.0f, 100.0f, 100.0f)), argsBuffer);
    }

    void OnGUI() 
    {
        GUI.Label(new Rect(265, 25, 200, 30), "Instance Count: " + instanceCount.ToString());
        instanceCount = (int)GUI.HorizontalSlider(new Rect(25, 20, 200, 30), (float)instanceCount, 1.0f, 5000000.0f);
    }

    void UpdateBuffers() 
    {
        // Ensure submesh index is in range
        if (instanceMesh != null)
        { 
            subMeshIndex = Mathf.Clamp(subMeshIndex, 0, instanceMesh.subMeshCount - 1);
        }

        // Positions
        if (positionBuffer != null)
        { 
            positionBuffer.Release();
        }

        positionBuffer = new ComputeBuffer(instanceCount, 16);
        Vector4[] positions = new Vector4[instanceCount];

        for (int i = 0; i < instanceCount; i++) 
        {
            float angle = Random.Range(0.0f, Mathf.PI * 2.0f);
            float distance = Random.Range(20.0f, 100.0f);
            float height = Random.Range(-2.0f, 2.0f);
            float size = Random.Range(0.05f, 0.25f);

            positions[i] = new Vector4(Mathf.Sin(angle) * distance, height, Mathf.Cos(angle) * distance, size);
        }

        positionBuffer.SetData(positions);
        instanceMaterial.SetBuffer("positionBuffer", positionBuffer);

        // Indirect args
        if (instanceMesh != null) 
        {
            args[0] = (uint)instanceMesh.GetIndexCount(subMeshIndex);
            args[1] = (uint)instanceCount;
            args[2] = (uint)instanceMesh.GetIndexStart(subMeshIndex);
            args[3] = (uint)instanceMesh.GetBaseVertex(subMeshIndex);
        }
        else
        {
            args[0] = args[1] = args[2] = args[3] = 0;
        }

        argsBuffer.SetData(args);

        cachedInstanceCount = instanceCount;
        cachedSubMeshIndex = subMeshIndex;
    }

    void OnDisable() 
    {
        if (positionBuffer != null) positionBuffer.Release();
        positionBuffer = null;

        if (argsBuffer != null) argsBuffer.Release();
        argsBuffer = null;
    }
}

InstancedShader.shader

//from https://docs.unity3d.com/2021.1/Documentation/ScriptReference/Graphics.DrawMeshInstancedIndirect.html
Shader "Instanced/InstancedShader" 
{
    Properties 
    {
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
    }

    SubShader 
	{

        Pass 
		{

            Tags {"LightMode"="ForwardBase"}

            CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_fwdbase nolightmap nodirlightmap nodynlightmap novertexlight
            #pragma target 4.5

            #include "UnityCG.cginc"
            #include "UnityLightingCommon.cginc"
            #include "AutoLight.cginc"

            sampler2D _MainTex;

            #if SHADER_TARGET >= 45
              StructuredBuffer<float4> positionBuffer;
            #endif

            struct v2f
            {
                float4 pos : SV_POSITION;
                float2 uv_MainTex : TEXCOORD0;
                float3 ambient : TEXCOORD1;
                float3 diffuse : TEXCOORD2;
                float3 color : TEXCOORD3;
                SHADOW_COORDS(4)
            };

            void rotate2D(inout float2 v, float r)
            {
                float s, c;
                sincos(r, s, c);
                v = float2(v.x * c - v.y * s, v.x * s + v.y * c);
            }

            v2f vert (appdata_full v, uint instanceID : SV_InstanceID)
            {
            #if SHADER_TARGET >= 45
                float4 data = positionBuffer[instanceID];
            #else
                float4 data = 0;
            #endif

                float rotation = data.w * data.w * _Time.x * 0.5f;
                rotate2D(data.xz, rotation);

                float3 localPosition = v.vertex.xyz * data.w;
                float3 worldPosition = data.xyz + localPosition;
                float3 worldNormal = v.normal;



                float3 ndotl = saturate(dot(worldNormal, _WorldSpaceLightPos0.xyz));
                float3 ambient = ShadeSH9(float4(worldNormal, 1.0f));
                float3 diffuse = (ndotl * _LightColor0.rgb);
                float3 color = v.color;

                v2f o;
                o.pos = mul(UNITY_MATRIX_VP, float4(worldPosition, 1.0f));
                o.uv_MainTex = v.texcoord;
                o.ambient = ambient;
                o.diffuse = diffuse;
                o.color = color;
                TRANSFER_SHADOW(o)
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                fixed shadow = SHADOW_ATTENUATION(i);
                fixed4 albedo = tex2D(_MainTex, i.uv_MainTex);
                float3 lighting = i.diffuse * shadow + i.ambient;
                fixed4 output = fixed4(albedo.rgb * i.color * lighting, albedo.w);
                UNITY_APPLY_FOG(i.fogCoord, output);
                return output;
            }

            ENDCG
        }
    }
}

InstancedSurfaceShader.shader

//from https://docs.unity3d.com/2021.1/Documentation/ScriptReference/Graphics.DrawMeshInstancedIndirect.html
Shader "Instanced/InstancedSurfaceShader" 
{
    Properties 
	{
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }

    SubShader 
	{
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model
        #pragma surface surf Standard addshadow fullforwardshadows
        #pragma multi_compile_instancing
        #pragma instancing_options procedural:setup

        sampler2D _MainTex;

        struct Input {
            float2 uv_MainTex;
        };

    #ifdef UNITY_PROCEDURAL_INSTANCING_ENABLED
        StructuredBuffer<float4> positionBuffer;
    #endif

        void rotate2D(inout float2 v, float r)
        {
            float s, c;
            sincos(r, s, c);
            v = float2(v.x * c - v.y * s, v.x * s + v.y * c);
        }

        void setup()
        {
        #ifdef UNITY_PROCEDURAL_INSTANCING_ENABLED
            float4 data = positionBuffer[unity_InstanceID];

            float rotation = data.w * data.w * _Time.y * 0.5f;
            rotate2D(data.xz, rotation);

            unity_ObjectToWorld._11_21_31_41 = float4(data.w, 0, 0, 0);
            unity_ObjectToWorld._12_22_32_42 = float4(0, data.w, 0, 0);
            unity_ObjectToWorld._13_23_33_43 = float4(0, 0, data.w, 0);
            unity_ObjectToWorld._14_24_34_44 = float4(data.xyz, 1);
            unity_WorldToObject = unity_ObjectToWorld;
            unity_WorldToObject._14_24_34 *= -1;
            unity_WorldToObject._11_22_33 = 1.0f / unity_WorldToObject._11_22_33;
        #endif
        }

        half _Glossiness;
        half _Metallic;

        void surf (Input IN, inout SurfaceOutputStandard o) {
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex);
            o.Albedo = c.rgb;
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}