Markup expenses switch is hidden by default. If you want it to be vsible when creating new projects or editing existing projects, you have to change Preempt Global Settings.
Go to Setup.
Use the search bar to find Preempt Global Settings.
Click on Manage button.
Click on Global.
Click on the Edit button.
Look for Show Markup Expenses Option (Use Ctrl+F). Check the box.
Click on Save.
Now, when editing or creating a project, the Markup Expenses switch will be visible.
Markup Expenses switch off - all expenses added to the project at cost.
Markup Expenses switch on - margin can be added to expenses.