Display Screen or a Portion Thereof with a Graphical User Interface

FIG. 1 is a front view of a first image in a sequence of a display screen or a portion thereof with a graphical user interface showing my new design; and,

FIG. 2 is a front view of a second image thereof.

The dashed broken line perimeter in the drawings illustrate a display screen or portion thereof and forms no part of the claimed design. The remaining dashed broken lines in the drawings illustrate portions of the graphical user interface that form no part of the claimed design. The appearance of the images sequentially transition between the images shown in FIGS. 1 to 2 , wherein the process or period in which one image transitions to another image forms no part of the claimed design.