Is there a way to add items to an invoice automatically? Maybe based on a tag and date range?

Good afternoon, @jack-flint-gmail. 

Congrats on making your first post here in the Community! Let me share some details to help answer your question. 

I can see how beneficial this could be for your business. However, you can only add items manually to an invoice. 

You can check out this guide to help you in the future: Create invoices in QuickBooks Self-Employed. 

I hope this helps answer your question. If you have any other concerns, don't hesitate to ask. Have a great day!