Please try below
root/vendor/magento/module-catalog/view/adminhtml/templates/catalog/category/edit/form.phtml
Around line number 34
<form id="category_edit_form" action="<?php echo $block->getSaveUrl() ?>" method="post" enctype="multipart/form-data">
Replace with
<form id="category_edit_form" name="category_edit_form" action="<?php echo $block->getSaveUrl() ?>" method="post" enctype="multipart/form-data">
root/vendor/magento/module-catalog/view/adminhtml/templates/catalog/category/tree.phtml
around line number 472
$('form .messages').html(data.messages);
Replace with
$('[name="category_edit_form"] .messages').html(data.messages);
Make sure remove cache , set proper permission , run setup:upgrade before check.
Hope this helps.