We're having a business case to raise/create an invoice for group of projects under one customer and send a single copy of invoice to the client and same will be uploaded into GST portal. However, our current invoicing structure is one to one mapping i,e We're able to raise for single project but not for group of projects. Having said, requirement is for billable time sublist and need to source timecards of group of projects. Any thoughts on this would be appreciated

You could use group invoicing to do this but would need to make sales orders with the billable time (1 for each project) then invoice those SOs then group them together A little tedious but gets the job done