<select id ="select">
  <option id-"fr" value="1">Select </option>
  <option value="2">2 кнопки</option>
  <option value="3">5 кнопок</option>
</select>
<div id="someElement"></div>
const select = document.querySelector('#select');
const handleSelectChange = e => {
  if(e.target.value == 2){
    document.getElementById('someElement').innerHTML = "<button>Кнопка, 2 штуки</button>";
  };
  if(e.target.value == 3){
    document.getElementById('someElement').innerHTML = "<button>Кнопка, 5 штук</button>";
   };
};

select.addEventListener('change', handleSelectChange);

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External JavaScript

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