Toolbar broken, permission errors after permission changes After performing the most recent core update, which required me to temporarily disable layout builder, my admin toolbar somehow became grey and unformatted as shown below. I've tried changing the admin theme, rebuilding the cache, disabling CSS, etc. but to no avail. 

After updating, I ran the security check, which gave some apparently very bad advice about changing permissions of hundreds of files to 744. I followed the advice, which totally broke the site. After reading the various guidance on permissions, I restored permissions to the best recommended ones I could, find but there are still permission errors occurring in the logs, which may or may not be related to this issue.

13498   11/Jun 17:49   file   Error      The specified file 'temporary://fileiFPN8R' could not be copied because the destination directory is not properly configured. This may be caused by a problem with file or directory permiss
13497   11/Jun 17:49   file   Error      The file permissions could not be set on public://css.
13496   11/Jun 17:49   php    Warning    User warning: mkdir(): Permission Denied in Drupal\Component\PhpStorage\FileStorage-&gt;createDirectory() (line 145 of /home/public/core/lib/Drupal/Component/PhpStorage/FileStorage.php) #0 /h


What other troubleshooting steps can I perform short of attempting to restore a backup pre-update?
Issue was from the instructions at the top of the page of this top-ranked search result for Drupal permissions.

I did chmod -R 664 files for the files directory, which apparently wasn't sufficient to change all file permissions. Issue persisted until changing permissions it via find files -type f -exec chmod 664 {} \; as described here.