Display Screen or Portion Thereof with a Graphical User Interface

FIG. 1 is a front perspective view of a display screen or portion thereof with a graphical user interface, showing a first image in a sequence of the new design; FIG. 2 is a front view showing the first image in the sequence thereof; FIG. 3 is a front view showing a second image in the sequence thereof; FIG. 4 is a front view showing a third image in the sequence thereof; FIG. 5 is a front view showing the fourth image in the sequence thereof: FIG. 6 is a front view showing a fifth image in the sequence thereof; FIG. 7 is a front view showing a sixth image in the sequence thereof; and, FIG. 8 is a front view showing a seventh image in the sequence thereof. The inner broken line rectangle shows the display screen or portion thereof. Broken lines outside the display screen show the environment of a computing device. The remaining broken lines show portions of the graphical user interface. All broken lines form no part of the claimed design. The appearance of the transitional image sequentially transitions between the images shown in FIGS. 2 - 8 . The process or period in which one image transitions to another image forms no part of the claimed design.