As suggested here: https://github.com/PHPOffice/PhpSpreadsheet/discussions/4265#discussioncomment-11488292

The solution is:

if (method_exists($spreadsheet, 'setExcelCalendar')) {
    $spreadsheet->setExcelCalendar(Date::CALENDAR_MAC_1904);
} else {
    Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
}