PS – I chown www-data for the original error and it created that second error I mentioned, applying to the following files:
This is usually due to inconsistent file permissions.: wp-admin/js/postbox.min.js, wp-admin/js/common.js, wp-admin/js/postbox.js, wp-admin/js/common.min.js, wp-admin/includes/class-wp-filesystem-ftpext.php, wp-admin/includes/screen.php, wp-admin/includes/class-wp-filesystem-ftpsockets.php, wp-admin/users.php, wp-admin/about.php, license.txt, wp-login.php, readme.html, wp-includes/js/media-views.min.js, wp-includes/js/autosave.min.js, wp-includes/js/twemoji.js, wp-includes/js/wp-emoji.js, wp-includes/js/twemoji.min.js, wp-includes/js/wp-emoji.min.js, wp-includes/js/media-views.js, wp-includes/js/wp-emoji-release.min.js, wp-includes/js/wp-emoji-loader.min.js, wp-includes/js/autosave.js, wp-includes/js/wp-emoji-loader.js, wp-includes/formatting.php, wp-includes/general-template.php, wp-includes/nav-menu-template.php, wp-includes/post.php, wp-includes/link-template.php, wp-includes/shortcodes.php, wp-includes/functions.php, wp-includes/class-wp-xmlrpc-server.php, wp-includes/class-wp.php, wp-includes/version.php, wp-includes/category-template.php, wp-includes/media.php, wp-includes/class-oembed.php, wp-includes/query.php, wp-includes/certificates/ca-bundle.crt, wp-includes/class-IXR.php, wp-includes/class-wp-walker.php, wp-includes/class-phpmailer.php, wp-includes/class-smtp.php, wp-includes/class-wp-theme.php, wp-includes/taxonomy.php, wp-includes/comment-template.php, wp-includes/widgets.php, wp-includes/update.php, wp-includes/comment.php, wp-config-sample.php