It is required to have DWP Subscription for Configuration Projects development.
The functionality that requires the DWP Subscription though, is to record your configurations in a Configuration Project and easily transfer it to another environment. The bug currently allows using this feature even without a DWP Subscription.
The bug will be fixed as Hotfix and the fix will be part of the next 10.0.4 release automatically.
To avoid confusion, we would like to inform you that this is an unintended bug, and Configuration Packaging Projects are part of the DWP Subscription only as announced several times and very prominently at the Release Days in January 2021.
What is available without DWP Subscription?
All Customers do and will have the ability to install, update and uninstall Extensions (Configuration Packages) that does not require a dedicated license (or license is present at customer system) from the Extension Gallery even without the DWP Subscription. It is intended behavior because we are planning to migrate all Marketplace Apps and 3-rd Party Extensions to be installed and updated via this Technology.
Private and Community Extensions are available only with DWP Subscription.