JSFiddle - React, Tailwind, and code Playground

HTML

<select><option value='1' selected>1</option></select>
<select><option value='1' selected>1</option></select>

JavaScript

$(function () {
    $('body').append('<br>Expect true: ' + $('select').is('[value=1]'));      // Multiple selects, returns true
    $('body').append('<br>Expect true:' + $('select').eq(0).is('[value=1]'));// Single select, returns false
    
    $('body').append('<br>Expect 2: ' + $('select').filter('[value=1]').size()); 
    $('body').append('<br>Expect 1: ' + $('select').eq(0).filter('[value=1]').size()); // Bug is not specific to is() function...
}());