Adding more than four jobs in QuickBooks Desktop is available, @Cheftel.

Make sure to make the job name different to successfully add one. It would be helpful as well if you can provide any prompt or error message after adding the 5th job. 

Let's try opening a sample file to check if you can add more than four jobs. I'll show you how:

1. In your QuickBooks Desktop, go to the  File menu at the top left portion.
2. Choose Close Company
3. In the No Company Open window, select the drop-down arrow beside Open a sample file
4. Select Sample product-based business.
5. Click OK and then choose I’m not the admin.
6. Once done, select Continue and then click OK.

 If it works, let's go back to your company file and run the Verify and Rebuild Data.

You'll want to track the expenses for a job. I've added this article for more details: Tracking job costs in QuickBooks Desktop.

Please leave a comment below if you need further assistance in adding customer jobs. I'm always available to assist you.