Hello, john135.
Thanks for stopping by the QuickBooks Community. Currently, the Markup feature is only used with billable expenses on the vendor side. So when you have billable time or changes that you pass on to the customer, you're able to set a markup for when you invoice that customer. I recommend sending a product suggestion though this link. Here you can provide feedback to our product developer team.
In the meantime. I'm adding a few helpful articles that you may find insightful.
If there's anything else I can help with in the meantime, feel free to reach out below.
Thanks again and have a lovely day.