You need to use value as well as disabled.
In this case, the initial value of v-model needs to match the value of the disabled one.

<div id="app">
  <select id='select-id' v-model='position'>
    <option disabled value="">Select option</option>
    <option>Opt 1</option>
    <option>Opt 1</option>
  </select>
</div>

var app = new Vue({
  el: '#app',
  data: {
    position: '',
  },
});

If the initial value of your v-model expression does not match any of the options, the element will render in an “unselected” state. On iOS this will cause the user not being able to select the first item because iOS does not fire a change event in this case. It is therefore recommended to provide a disabled option with an empty value, as demonstrated in the example above.

Documentation