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$users = \Bitrix\Main\UserGroupTable::getList( [
    'select' => [ 'USER_ID' ],
    'filter' => [
        '=GROUP_ID'    => 7,
        '=USER.ACTIVE' => true,
    ],
] )->fetchAll();

$users = array_map( static function ($user) {
    return (int) $user['USER_ID'];
}, $users );

$this->SetVariable( 'Variable1', $users);