Parallels 12 on MacOS has a curiously misleading UI issue on the VM configuration dialog, where the items in the left list are actually a scrollable list, but there’s no visual indication that tells you this:
If you click in the list to highlight an item, you can scroll the list up and down to reveal other items – in this case I was looking for the Boot Order setting, but it was displayed at the top of the list and I needed to scroll the list up to see it:
