Rather than re-explaining the whole process that got me here, I'm hoping I can just reference this question: Can't access specific admin pages
In that question, I was hitting errors while trying to update Drupal. I updated composer as well.
After clearing caches, restarting PHP and restarting my docksal project, the errors went away, and the admin seems usable except the specific thing I need
A backup tar was lost during all of that, so I'm trying to create a new back-up, so I'm back to safety. But, when I go to the export page, here: page /admin/config/development/configuration/full/export, I click the export button, and it gives me a fatal error:
Fatal error: Class 'Archive_Tar' not found in /var/www/docroot/core/lib/Drupal/Core/Archiver/ArchiveTar.php on line 8
When I look in the log, I see this message:
The file /tmp/config.tar.gz was not deleted because it does not exist.
This is Drupal 8.7.3 , if that helps.
I would just do
drush archive-backup, if I could. But that option has ben removed.
Not sure if I gave enough info, above. Let me know.