When you upgrade from DU Meter 7 to DU Meter 8, DU Meter Taskbar Band will be closed to allow the program files to be replaced, and there is no Microsoft-approved way to re-enable it automatically afterwards. Therefore, it should be enabled manually:

On Windows 10

Right-click on any empty space on the Windows taskbar, select the top "Toolbars" submenu, and then select "DU Meter" from that submenu.

On Windows 11

Taskbar band is no longer supported on Windows 11 and cannot be re-enabled. Microsoft decided to remove this feature from Windows 11.