Man kann über eine DialogFunction xlsx generieren.
Man sammelt die Daten in einer Map und macht dann im JS so etwas in der Richtung (verkürzt aus einem Projekt und ungetestet)

JS:

jr_execute_dialog_function(
                'getXlsx',
                { data: data },
                function(/** @type {{ status: string; result: { data: string; }; }} */ response) {
                    if (response.status === 'ok') {
                        var a = document.createElement('a');
                        a.download = 'export.xlsx';
                        a.href =
                            'data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,' +
                            response.result.data;
                        a.click();
                    } else {
                        handleError(response);
                    }
                },
                handleError
            );

PHP

<?php

class className extends JobRouter\Engine\Runtime\PhpFunction\DialogFunction
{
    public function execute($rowId = null)
    {
        require_once(Utility::getJobRouterPath() . '\library\vendor\phpoffice\phpspreadsheet\src\Bootstrap.php');
        $spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
        $spreadsheet->getActiveSheet()->fromArray($this->getParameter('data'));

        ob_start();
        (new \PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet))->save('php://output');
        $this->setReturnValue('data', base64_encode(ob_get_clean()));
    }
}