How to pass an array of unfixed size to a shader?

Just started learning shader programming and I can't figure out how to do this. I know how to pass an array of fixed size to a shader.

This script passes the array to the shader:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 // Whenever "sizeOfShaderArray" is changed, this script will update the _Array property of the shader
 public class ArrayShaderScript : MonoBehaviour {
     
     public int sizeOfShaderArray = 20;
 
     [ExecuteInEditMode]
     void Awake()
     {
         InitializeArray();
     }
 
     void OnValidate()
     {
         InitializeArray();
     }
 
     private void InitializeArray()
     {
         // Initialize the array with data
         float[] data = new float[sizeOfShaderArray];
         for (int i = 0; i < sizeOfShaderArray; i++)
             data[i] = 0.5f;
 
         // Add the array to the material.
         MaterialPropertyBlock arrayPropertyBlock = new MaterialPropertyBlock();
         arrayPropertyBlock.SetFloatArray("_Array", data);
         GetComponent<Renderer>().SetPropertyBlock(arrayPropertyBlock);
     }
 }

And this is how I define and use the array in my shader script:

 sampler2D _MainTex;
 float _Array[20]; // Instead of having a fixed size, I want this to be my "sizeOfShaderArray" variable in the ArrayShaderScript.
 
 fixed4 frag (v2f i) : SV_Target
 {
     fixed4 col = tex2D(_MainTex, i.uv);
 
     col *= _Array[5]; // Do stuff with array here
 
     return col;
 }