'All Internal Users' is not available within a List View

Enable Partner Relationship Management in Salesforce Classic

To force this option to become available, please, switch the User Interface back to "Classic" and follow the clickpath below:

Setup - Customize - Partners - Setting and activate Enable Partner Relationship Management

Create a Public Group

If you do not have access to the "Classic" user interface, we suggest creating a public group that includes all internal users, and creating your list sharing options based upon that public group.