Example of setting TextMeshPro text every frame without allocations

NumberStringsTesting

using System.Collections.Generic;
using TMPro;
using UnityEngine;

public class NumberStringsTesting : MonoBehaviour
{
    public List<TMP_Text> digits; //Add these in reverse order (Highest digit first, lowest digit last)

    List<int> numbers = new List<int>(50);

    void Start()
    {
        for (int i = 0; i < 50; i++)
        {
            numbers.Add(0);
        }
    }

    void Update()
    {
        int num = (int)Time.realtimeSinceStartup;
        int index = 0;
        while (num > 0)
        {
            numbers[index] = num % 10;
            num = num / 10;
            index++;
        }

        for (int i = 0; i < index + 1; i++)
        {
            digits[i].SetText(NumberStrings.Zero_To_Nine_Strings[numbers[i]]);
        }
    }
}

public class NumberStrings
{
    public static string[] Zero_To_Nine_Strings = new string[] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9" };
    public static char[] Zero_To_Nine_Chars = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
}