Display Screen or Portion Thereof with a Graphical User Interface

The file of this patent contains at least one drawing/photograph executed in color. Copies of this patent with color drawing(s)/photograph(s) will be provided by the Office upon request and payment of the necessary fee. FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface; FIG. 2 is another embodiment thereof; FIG. 3 is another embodiment thereof; FIG. 4 is another embodiment thereof; FIG. 5 is another embodiment thereof; and, FIG. 6 is another embodiment thereof. The outer perimeter shown in broken lines in the figures illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining broken lines in the figures illustrate portions of the graphical user interface that form no part of the claimed design. The grayscale in the figures indicates a contrast of appearance.