Center lines of strokes will be hidden if the Pan (View), Zoom, Color Picker or Measure tool is selected, but reappear once another tool is selected even though no objects are selected. Center lines of strokes are not shown when a document is initially opened, only after being selected. This issue is not effected by stroke width or visibility or even if the objects opacity is set to 0%.
Designer V1 would only show the stroke center lines (in blue) for a selected object(s). Once an object was deselected the center line would disappear.
Using macOS Monterey, V 12.6.1, Mac mini (Late 2014)