Does SharePoint have the ability of adding addition details to a grouped by listing?

Jamie_Hogan You can use the SharePoint JSON view formatting to customize the display of grouped list view.

Check below documentations: 

1. view-group-formatting 
2. Build custom group headers and footers 

Few more examples given at: 

1. Remove column name from group header 
2. Group Header Status Icon and Color 
3. List-Formatting view-samples 

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