IntelliJ grayed out Run Configuration

A dimmed run configuration simply means it hasn't been saved. Technically called "temporary run configurations" by the IntelliJ manual:

Temporary configurations are marked with semi-transparent icons and are managed same way as the permanent configurations. By default, 5 temporary configurations are allowed per project. You can change this limit via the Edit Configurations dialog.

Saving (which makes the config permanent) can be done in either the "Run/Debug Configurations" menu (visible only when selected), or in the config selection dropdown in the general UI:

After saving, the configuration will move up to group with the reset of the saved configurations and will no longer be dimmed. As far as I can tell, you can have as many saved configs that you want.