I'm here to help share some information about using the Project feature in QuickBooks Online.
Once the status of a project is completed, it will still show up in the timesheet. You are correct, at this time, there's no option yet to hide a completed or canceled projects unless you make the customer inactive.
I'd suggest sending feedback to our Product Developers to consider this option for the future update. I'll also send one to make the Project feature in QBO better. You can send your suggestion directly on this link: https://feedback.qbo.intuit.com/forums/168199.
You can also check out the following articles below for further information about the Projects feature in QBO:
I'm always here to help if you have other questions about the Projects feature. Have a nice weekend.