JSFiddle - React, Tailwind, and code Playground

HTML

<input type="checkbox" value= "checkbox1" name="checkbox1" id="checkbox1">

    <div class="select">
<select id="dropdown" name="dropdown" multiple="multiple">
    <option id="item">My Item</option>
</select>
    </div>

CSS

.select {
    display: none;
}

JavaScript

$( 'document' ).ready(function () {
    
    // When checkbox clicked
    $('input#checkbox1').click( function(){
        
        // If has been checked or unckecked
        if ($('input#checkbox1').is(':checked')) {
            
            // Smoothly animate the div in
            $( ".select" ).slideDown( "slow" );
        } else {
            
            // Smoothly animate the div away
            $( ".select" ).slideUp( "slow" );
        }
    });
});