When you open or expand a category, the dropdown shows the category but then it closes/retracts again by itself.
It only closes or retracts itself after the other dropdown section has been clicked.
$(document).ready(function() {
$('li.right-menu').click(function() {
$('li.right-menu').not(this).find('ul').hide();
$(this).find('ul').toggle();
});
});<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.1/jquery.min.js"></script>
<ul>
<li id="rm1" class="right-menu">
<a VEHICLES</a>
<ul id="testCat" class="cat-mega-menu cat-mega-menu-4" style="z-index: 3;">
<li id="rm2" class="right-menu cat-mega-title">
<ul id="dsp" class="listdsp" target="1">
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item </a></li>
<li><a>list Item</a></li>
</ul>
</li>
<li class="right-menu cat-mega-title">
<ul>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item </a></li>
<li><a>list Item</a></li>
</ul>
</li>
<li class="right-menu cat-mega-title">
<ul>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item</a></li>
<li><a>list Item </a></li>
<li><a>list Item</a></li>
</ul>
</li>
</ul>
</li>
</ul>