I kept getting messages on my Acquia Dev Desktop 2 installation of 8.3.1 on Windows 10 that there were critical updates needed. So I followed the instructions at https://www.drupal.org/docs/7/updating-your-drupal-site/how-to-update-dr…. I made a backup copy of everything in ~Sitesdevdesktopdrupal-8.3.1, went into maintenance mode, used Dev Desktop to stop Apache and MySQL, then copied everything except sites from the 8.3.4 zip download to ~Sitesdevdesktopdrupal-8.3.1, but the site wouldn’t come back up.
Then I thought I should have followed the instructions at https://www.drupal.org/node/2700999. Thought I could reverse my damage be shutting down Apache and MySQL again, changing the name of ~Sitesdevdesktopdrupal-8.3.1 to drupal-8.3.1bad, changing the name of ~Sitesdevdesktopdrupal-8.3.1-Copy back to drupal-8.3.1, and restarting Apache and MySQL. But all I get from my site is 500 Internal Server Error. Can I salvage this?
I have a second site here that I made when trying out Acquia’s Lightning package which still works. But if I can figure out how to recover my first site, I won’t lose my progress on Acquila’s YouTube tutorial.