Hello there, @carsten1. Welcome to the Community.
I want to make sure to cover every concern you have here in the Community. I'd like to ask for further details of your concern. This way, I can provide the exact resolution for it.
In the meantime, I'm adding this article to learn more about the Projects feature in QBO: Projects FAQ. It answers the most frequent;y asked questions about the feature like reports and budget by project, to name a few.
I'm just around to help if you have other project concerns or inquiries about managing inventories in QBO. Take care always.