JSFiddle - React, Tailwind, and code Playground

HTML

<select>
  <option value="1">1</option>
  <option value="2">2</option>
  <option value="3">3</option>
  <option value="4">4</option>
  <option value="5">5</option>
  <option value="6">6</option>
  <option value="7">7</option>
  <option value="8">8</option>
  <option value="9">9</option>
  <option value="10">10</option>
</select>

JavaScript

var x = 5; // граница, ищем числа меньше этого числа

$('select').on('change', go);

function go() {
  var index = this.selectedIndex; 
 	while(index) {
  	if(this.options[index].value < x) break;
    index--;
  }
  
  var maxValue = this.options[index].value;
  console.log(maxValue);
}