Within the desktop application, an invoice cannot be created directly via a bulk action; however, it is possible to link multiple orders to a single invoice.
We create an issued invoice (either via Sales - Issued Invoices - New or Sales - Received Orders - Services - Create Issued Invoice).
Additional orders can be added by clicking the arrow next to the "Add" option in the document line items section. Once expanded, you will see the option "Order Invoicing". Using this function, you can link the issued invoice to multiple orders.
If you use the warehouse module, you can create stock issue slips for your orders and then use the bulk issued invoice function under Services to generate a single issued invoice for all selected stock issue slips.
Multiple orders can be consolidated into a single invoice via the API — see the guide.