Use a select for a single choice from about five to fifteen options. Fewer: a radio group or a segmented control, so every option is visible. Many more, or options worth searching: the combobox (coming later).
Group long lists with <optgroup>. aria-invalid, disabled and multiple work as they do on a text field.
Accessibility
It's the native element: keyboard, screen reader and touch behaviour are the platform's own, and phones show their native picker.
A placeholder option ("Choose a region") is a real, disabled, selected option with an empty value, so a required select still validates.
The chevron is a background image; in forced-colours mode the browser's own arrow returns.