Export feature is obsolete
This is probably a known issue, but it wasn't documented. So here it goes...
While composer advises against using
PhpExcel, it looks like
phpoffice/phpexcel could be added back the
composer.json file and work alongside
phpoffice/phpspreadsheet. A better alternative would be to migrate the export2excel2007 method to
phpspreadsheet, perhaps using its migration tool.