Defs,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
</head>
<body>
<ul class="select2-r">
<li class="select2-rs">
<div class="select2-rl">
<span class="select2-m"></span>
All
</div>
</li>
<li class="select2-rs">
<div class="select2-rl">
<span class="select2-m"></span>
Иванов (43)
</div>
</li>
<li class="select2-rs">
<div class="select2-rl">
<span class="select2-m"></span>
Зайков (18)
</div>
</li>
<li class="select2-rs">
<div class="select2-rl">
<span class="select2-m"></span>
Петров (11)
</div>
</li>
<li class="select2-rs">
<div class="select2-rl">
<span class="select2-m"></span>
Сидоров (24)
</div>
</li>
........
</ul>
<script>
const divs = [...document.querySelectorAll(".select2-rl")];
const reg = /(?<name>[а-яё]+)\s+\((?<number>\d+)\)/i;
const obj = divs.reduce((ob, div) => {
const groups = div.textContent.match(reg);
if(groups) {
const {name, number} = groups.groups;
ob[name] = number;
}
return ob
}, {})
alert(obj.Сидоров)
</script>
</body>
</html>