Texture2D Array example, see https://docs.unity3d.com/ScriptReference/Texture2DArray.html

TextureArray.cs

// Used to generate Texture Array asset
// Menu button is available in GameObject > Create Texture Array
// See CHANGEME in the file
using UnityEngine;
using UnityEditor;

public class TextureArray : MonoBehaviour {

    [MenuItem("GameObject/Create Texture Array")]
    static void Create()
    {
        // CHANGEME: Filepath must be under "Resources" and named appropriately. Extension is ignored.
        // {0:000} means zero padding of 3 digits, i.e. 001, 002, 003 ... 010, 011, 012, ...
        string filePattern = "Smoke/smoke_{0:000}"; 
        
        // CHANGEME: Number of textures you want to add in the array
        int slices = 24;
        
        // CHANGEME: TextureFormat.RGB24 is good for PNG files with no alpha channels. Use TextureFormat.RGB32 with alpha.
        // See Texture2DArray in unity scripting API.
        Texture2DArray textureArray = new Texture2DArray(256, 256, slices, TextureFormat.RGB24, false);
        
        // CHANGEME: If your files start at 001, use i = 1. Otherwise change to what you got.
        for (int i = 1; i <= slices; i++)
        {
            string filename = string.Format(filePattern, i);
            Debug.Log("Loading " + filename);
            Texture2D tex = (Texture2D)Resources.Load(filename);
            textureArray.SetPixels(tex.GetPixels(0), i, 0);
        }
        textureArray.Apply();

        // CHANGEME: Path where you want to save the texture array. It must end in .asset extension for Unity to recognise it.
        string path = "Assets/Tasmania/Resources/SmokeTextureArray.asset";
        AssetDatabase.CreateAsset(textureArray, path);
        Debug.Log("Saved asset to " + path);
    }
}

// After this, you will have a Texture Array asset which you can assign to the shader's Tex attribute!

TextureArray.shader

// Directly taken from Unity doco
Shader "Example/Sample2DArrayTexture"
{
	Properties
	{
		_MyArr("Tex", 2DArray) = "" {}
		_SliceRange("Slices", Range(1,24)) = 0
		_UVScale("UVScale", Float) = 1.0
	}
	SubShader
	{
		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			// to use texture arrays we need to target DX10/OpenGLES3 which
			// is shader model 3.5 minimum
			#pragma target 3.5

			#include "UnityCG.cginc"

			struct v2f
			{
				float3 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
			};

			float _SliceRange;
			float _UVScale;

			v2f vert(float4 vertex : POSITION)
			{
				v2f o;
				o.vertex = mul(UNITY_MATRIX_MVP, vertex);
				o.uv.xy = (vertex.xy + 0.5) * _UVScale;
				o.uv.z = (vertex.z + 0.5) * _SliceRange;
				return o;
			}

			UNITY_DECLARE_TEX2DARRAY(_MyArr);

			half4 frag(v2f i) : SV_Target
			{
				return UNITY_SAMPLE_TEX2DARRAY(_MyArr, i.uv);
			}
			ENDCG
		}
	}
}