Click Show/Hide Lineweight Find on the status bar.
The status bar is located in the lower right-hand corner of the application window.
Note: If the Show/Hide Lineweight button is not visible, click Customization, the right-most button on the status bar, to add it to the status bar.
Find
If no change is visible, it's probably due to a combination of the thickness of the line compared to the display resolution of your monitor.