Drupal 8.5 broken after simultaneously enabling many modules
In the Drupal Slack channel, it was suggested I should try disabling modules using drush, starting with Devel since that appeared to be where the problem was coming from.  After

# drush pm-uninstall devel
The following extensions will be uninstalled: devel, ds_devel
Do you really want to continue? (y/n): y
devel was successfully uninstalled.                 [ok]
ds_devel was successfully uninstalled.              [ok]


the site's user interface came back to life, and I was able to install all of the modules I had previously selected, including Devel and Display Suite Devel.

I strongly suspect what happened is the error that terminated the initial attempt to enable modules

Maximum execution time of 30 seconds exceeded in /web/spacecolonists/drupal/vendor/symfony/dependency-injection/ContainerBuilder.php on line 1005


occrured in the middle of processing the Devel installation, which broke it.

This tells me that module installations are not done as a transaction:  If they were, the timeout error would have caused the database transaction to fail, resulting in a rollback that left the database in a stable, working state.