Optional End Date
This module makes the end date field in a date range field type optional. It adds a checkbox to the field's storage settings, allowing users to create date ranges without specifying an end date. This functionality is intended to be a temporary solution until Drupal core implements the same feature.
Make the end date in a Date range field (DateRangeItem) optional.
An extra "Optional end date" checkbox is added to the Date range field type
Storage settings. When the box is checked, the end date is no longer required.
This will mimic the behavior of optional end dates in future Drupal versions. So when
#2794481: Allow end date to be optional is ready, you should be able to uninstall this module after updating, and
use the core implementation instead.
See https://www.drupal.org/project/drupal/issues/2794481 for more information
about the core implementation.