For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
$app = JFactory::getApplication();
$files = $app->input->files->get('yourtable___yourelement', array(), 'raw');
$name = ArrayHelper::getValue($files, 'name', '');
http://fabrikar.com/forums/index.php?wiki/php-list-plugin/#accessing-the-selected-rows-dataPHP code - If no file selected then the php code entered in this textarea will be run. Do not encase your PHP code with "<?php ?>".
IMPORTANT:placeholders like {element___table}, {rowid} etc are not usable here and in php file, neither