Display screen or portion thereof with a graphical user interface

FIG. 1 is a front view of a first image in a sequence for a display screen with a graphic user interface showing my new design;

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

FIG. 3 is a front view of a third image thereof;

FIG. 4 is a front view of a first image of a second embodiment thereof;

FIG. 5 is a front view of a second image of the second embodiment thereof; and,

FIG. 6 is a front view of a third image of the second embodiment thereof.

The broken lines around the Figures showing a display screen or portion thereof are included for the purpose of illustrating environmental structure. The broken line showings of the text, numbers, symbols, function marks, and images in Figures are included for the purpose of illustrating portions of the display screen with a graphic user interface. The broken lines form no part of the claimed design. The transitional images sequentially transition between the images shown in FIGS. 1-3 and FIGS. 4-6 . The process, sequence, or period in which one image transitions to another image forms no part of the claimed design.