JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="filter">
<select id="OrganisationDDL">

<option value=1076453>First</option>
<option value=1076453>Code</option>
<option value=1076453>City</option>
<option value=1076453>Option</option>
<option value=1076453>Fake</option>
<option value=1076453>Look<option>
<option value=1076453>Never</option>
<option value=1076453>Ever</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option value=1076453>Second</option>
<option...

JavaScript

function FilterOrganisations(selectedText, DDL, skipFirstItem = true)
{
    var rval = selectedText.toUpperCase();

    var i = skipFirstItem ? 1 : 0;
    for (; i < DDL.length; i++) {
        var currentItem = DDL.item(i);

        var lval = currentItem.innerText.toUpperCase();
        
        if(lval.includes(rval))
        {
            currentItem.style = "display: block;";
        }
        else
        {
            currentItem.style = "display: none;";
        }

        DDL[i] = currentItem;
    }
}


    p_orgDLL = document.getElementById("OrganisationDDL");
    p_filterOrganisations = document.getElementById("filter"); 
    p_filterOrganisations.onchange = function()
    { 
        FilterOrganisations(p_filterOrganisations.value, p_orgDLL);
    }