The ornamental design for display panel or portion thereof with a graphicaluserinterface, as shown and described.
The sole FIGURE is a front view of a display panel or portion thereof with a graphical user interface showing a design.
The subject matter of the present disclosure includes graphical user interface components present. The broken lines depicting a display panel or portion thereof are included for the purpose of illustrating environmental structure and form no part of the design. The broken lines depicting portions of a graphical user interface are included for illustrating environmental aspects of a display panel or portion thereof with a graphical user interface and form no part of the design.