Deleting a project won't affect your reporting data, Musery. It's because we want to make sure your books are intact in QuickBooks Online (QBO).

The transactions associated with the project will still appear on your financial reports, such as Profit and Loss Detail. However, there's a (deleted) tag beside them. I've attached a screenshot below on how it looks like in QBO. 

Moreover, you can reactivate the deleted project if you want to use it again. Just go back to the Projects menu to complete this task. You can also refer to the steps provided by rachel above. For detailed instructions, see the Can I delete a project? section through this article: Projects FAQ. 

I'll be right here to help if you need anything else. Enjoy the rest of your day, Musery.