Display Screen or a Portion Thereof with a Graphical User Interface

FIG. 1 is a front view of an embodiment of the display screen or a portion thereof with a graphical user interface; and, FIG. 2 is a front view of another embodiment of the display screen or a portion thereof with a graphical user interface. The outer dot-dash-dot broken lines show a display screen or a portion thereof and are for the purpose of illustrating environment and form no part of the claimed design. The broken lines show portions of the graphical user interface and are for the purpose of illustrating environment and form no part of the claimed design.