Hello there, NeuroManager.
I appreciate you for joining this thread.
Are you referring to the first screenshot above? If so, the markup option is only available when you create a Bill. As mentioned by my colleague, if you wish to pass the billable time or expense to a customer, you can use the markup you created and apply to an invoice.
While the mark up option in QuickBooks Online can only be use with billable expense on the vendor side, you can check out the QuickBooks Blog for product updates and new features available.
Should you have additional questions, feel free to let me know. I'd be delighted to help.