Dropdown lists just from two elements are pure evil.
Illustrator has one in the Keyboard Shortcuts dialog.

What’s a point of having it? Don’t you have enough space on the x-axis to display both items at once and improve the discoverability of both options?
As if you were hoping to get another item in that list and never added... in30 years.

Remake it into two conjoined toggle buttons, or at list in a radio-group (ugh), but just allow users to see both available options at once.