I am using a personal/test PowerApps environment with a CDS database. In the list of Entities there is a 'Tags' column alongside 'Entity' and 'Type', and the option to view the list grouped by them. From setup, the Tags used are:
Any entities I create are tagged 'Custom'. I cannot find a way to assign different or additional Tags. Is this possible?
those are by default, the tags represent what application the entity is coming from, in some of the cases they represent that are Out of the Box Dynamics 365 CE, Financials or Operations, the Tag Custom is that you are creating a Custom Entity that is not part of any application core entities, then this is normal, you can't change that.
In a custom entity you will see that some fields are System, these are created automatically by the system, and other fields are custom, those are the new fields you are adding to your custom entity.