JSFiddle - React, Tailwind, and code Playground

HTML

<div>
  <input class="next-input js-tracking-number-input" data-bind-event-input="debouncedSetTrackingNumber(this.value, 0, true)" data-bind="trackingNumber" autocomplete="on" size="30" type="text" name="fulfillments[0][shipping_options][tracking_number]" id="fulfillments_0_shipping_options_tracking_number">
</div>

<div>
  <input type="text" id="text-1179424fdf221cee11464f318f3e7613" autocomplete="on" data-searchable-select-input="true" class="next-input next-input--invisible" role="combobox" aria-label="Search and select an option for Shipping carrier" aria-expanded="false" aria-autocomplete="list" aria-owns="fulfillments_0_shipping_options_tracking_company-searchable-select">
</div>

JavaScript

function init() {
	const firstInputElement = document.getElementsByClassName('js-tracking-number-input')[0];
  
  	const secondInputElement = document.getElementsByClassName('next-input--invisible')[0];
  
  firstInputElement.oninput = (event) => {
    const inputValue = event.currentTarget.value;
    secondInputElement.value = /^[a-z]+/i.test(inputValue) ? 'Other' : ''
  };
}

init();