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 showing our new design;

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

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

FIG. 4 is a front view of a fourth embodiment thereof;

FIG. 5 is a front view of a fifth embodiment thereof;

FIG. 6 is a front view of a sixth embodiment thereof;

FIG. 7 is a front view of a seventh embodiment thereof;

FIG. 8 is a front view of an eighth embodiment thereof;

FIG. 9 is a front view of a ninth embodiment thereof;

FIG. 10 is a front view of a tenth embodiment thereof;

FIG. 11 is a front view of an eleventh embodiment thereof; and,

FIG. 12 is a front view of a twelfth embodiment thereof.

The outermost broken lines represent the display screen or portion thereof and form no part of the claimed design. The broken lines within the display screen represent text and graphical elements that form no part of the claimed design.