Board Thread:Technical Updates/@comment-24006128-20200311154142/@comment-1807002-20200316025956

NerdWithAKeyboard wrote:
 * No option to set editor defaults; I prefer source editor, and it always defaults to Visual Editor.

You have to disable visual editor in preferences (in the new UCP) but this will disable source editor on non-UCP wiki. It is a know bug (Thread:1823409).