// Created on savesnippets.com · https://savesnippets.com/6eT6C08SANoOdP
<?php
function uniqueBy(array $items, callable $keyFn): array {
    $seen = [];
    $out  = [];
    foreach ($items as $item) {
        $k = $keyFn($item);
        if (!array_key_exists($k, $seen)) {
            $seen[$k] = true;
            $out[]    = $item;
        }
    }
    return $out;
}

$users = [
    ['id'=>1,'name'=>'Alice'],
    ['id'=>2,'name'=>'Bob'],
    ['id'=>1,'name'=>'Alice (dup)'],
];

print_r(uniqueBy($users, fn($u) => $u['id']));
// [ {id:1,name:Alice}, {id:2,name:Bob} ]