Display Screen or Portion Thereof with a Graphical User Interface

FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface according to a first embodiment of the new design;

FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface according to a second embodiment of the new design;

FIG. 3 is a front view of a display screen or portion thereof with a graphical user interface according to a third embodiment of the new design; and,

FIG. 4 is a front view of a display screen or portion thereof with a graphical user interface according to a fourth embodiment of the new design.

The outermost rectangular broken line in the figures illustrates a display screen or portion thereof and forms no part of the claimed design. The remaining broken lines represent elements of the graphical user interface that form no part of the claimed design.