It's always comforting to know that I am working on a backup when I first attempt to update a module or Drupal core.
My Status Report said that I should update several modules, including Metatag. Updating the modules caused the site to break. The error message indicated that the problem was with the Metatag module. I extracted the backup again on my demo site, and repeated the process to be sure that I wasn't dealing with a one=time glitch. The problem occurred again.
After another extraction on my demo site, I checked further on the Status Report. There was a note that the Metatag update requires Drupal 8.8.5. I updated core and repeated the procedure - another failure.
A little research in Me Metatag issue queue showed that this has been a problem for others. The conventional wisdom was to clear cache using Drush. I have nevver been able to install Drush on my demo account, so that wasn't going to work.
Reading farther I found a reference to opening the site in another tab. I then opened the page <demosite>/<subsite>/admin - where demosite id the URL of the domain where I do my demos and tests and subsite is the folder where the demo version of the site I am working on is installed. Surprisingly, the admin page came up and I was able to flush the cache. The site was working again.