I would like to create a project where the incomes and the expenses are fake, so I can calculate the profit without affecting the balance

Hello there, @jprieguem-outloo.

When creating any transactions in QuickBooks Online, this will affect your bank balance since the entries are added and deducted to your bank account.

However, to get your work done, you may utilize a free trial version of QuickBooks Online Plus so you can enter dummy transactions and calculate the profit. This way, the balance of your real QBO account won't be affected. 

To subscribe to a free trial, you can select your version depending on the country that you're in, through this link: Choose your country.

After that, you may now turn on and start tracking projects by following these steps:

To turn projects:

1. Click on the Gear icon at the top.
2. Select on Company Settings.
3. Go to the Advanced tab.
4. Find the Projects section and select Edit ✎ to expand it.
5. Press the Organise all job-related activity in one place checkbox.
6. Hit on Save and close your settings.

Once done, here's how to create projects:

1. Tap on the Projects menu.
2. Select on New Project.
3. Give your project a memorable name.
4. Choose the customer you’re working for from the drop-down menu.
5. Add any notes or details about the project.
6. Hit on Save.

For complete details about this process together with adding income and expenses projects, please refer to this link: Learn how to use Projects to track project income, expenses, and profitability.

I'm also adding this article for your reference, which contains details about all you need to know regarding managing projects in QBO: Learn more about Projects in QuickBooks Online.

I'll be around to assist you further if you have any other concerns. I'd be happy to help. Have a good one!