The Standard Systems ActionInbox and AdHoc System got deleted in Universal Worklist - Configuration .
i.e System ActionInbox with connector type ActionInboxConnector &
AdHoc System with connector type AdHocWorkflowConnector
Please help with any link or document that contains the process of creation of these standard System in UWL.
The connectors should be available for selection when creating a New connector, in case you deleted the ActionInboxConnector and AdHocWofkflowConnector that come created by default in the UWL.
If that is the case and these connector types are not appearing in the drop down to select the connector type, in spite of yourself having already deleted the preconfigured ones, then you can try to restart the UWL application by following the steps from SAP KBA 1894284.
Please restart the whole UWL application, and check if the connectors types will be available for being selected when creating a new connector.
Hope this helps!