Display screen or portion thereof with a graphical user interface

FIG. 1 is a front view of the display screen or portion thereof with a graphical user interface in accordance with a first embodiment of our new design; and,

FIG. 2 is a front view of the display screen or portion thereof with a graphical user interface in accordance with a second embodiment of our new design.

The broken lines shown in the drawings represent portions of the display screen or portion thereof with a graphical user interface that form no part of the claimed design. Specifically, none of the broken lines, in any style, form part of the claimed design. Although multiple different styles of broken lines are shown, none of these broken lines in any of the various styles shown form part of the claimed design. In particular, dotted lines, dashed lines, and any other broken lines of any variety of line weights form no part of the claimed design. Likewise, the dotted pattern within the tubular bar, the dotted concentric circling, and the heavier dotted circle do not form part of the claimed design. Only the solid lines shown form the claimed design.