Thank you for joining the Community, nicola-lumal-co-.

I know how important it is to have this feature in QuickBooks Online mobile app. However, the project feature is currently unavailable in the mobile app. 

As a workaround, you can set it up through a browser using a different device like a laptop or a desktop.

Here's how:

1. Go to  Settings ⚙, then choose Account and settings.
2. Select the Advanced tab.
3. Look for the Projects section and select Edit ✎ to expand it.
4. Turn on Organise all job-related activity in one place.
5. Select Save and then Done.

Here's an article for more details about the project feature: Set up and create projects in QuickBooks Online.

I'm also adding this link to learn how you can add existing invoices to QuickBooks Online Projects.

Feel free to get back to me if you have other concerns about projects. I'll be in touch. Have a great day!