The details panel in Microsoft To Do is too narrow and I can't make it wider

A few months ago, something happened to my instance of Microsoft To Do. The "Details Panel" (I think that is the name) that appears on the right side of the screen when a task is selected is too narrow to even accommodate words more than a few letters long. (See photo) The only way I know to adjust this is to place the pointer along the border between the Details Panel and the Task List until it becomes a double arrowhead. However, while this feature ought to permit me to adjust the width of the Details Panel, it is now non-functional. Does anyone have any idea how can I fix this?