The ornamental design for a displayscreen or a portion thereof with a graphicaluserinterface, as shown and described.
FIG. 1 is a front view of a display screen or a portion thereof with a graphical user interface;
FIG. 2 is a front view of a second embodiment of a display screen or a portion thereof with a graphical user interface;
FIG. 3 is a front view of a third embodiment of a display screen or a portion thereof with a graphical user interface;
FIG. 4 is a front view of a fourth embodiment of a display screen or a portion thereof with a graphical user interface;
FIG. 5 is a front view of a fifth embodiment of a display screen or a portion thereof with a graphical user interface;
FIG. 6 is a front view of a sixth embodiment of a display screen or a portion thereof with a graphical user interface;
FIG. 7 is a front view of a seventh embodiment of a display screen or a portion thereof with a graphical user interface; and,
FIG. 8 is a front view of an eighth embodiment of a display screen or a portion thereof with a graphical user interface.
The broken lines showing a display screen or a portion thereof in all views form no part of the claimed design. The remaining broken lines showing portions of the graphical user interface form no part of the claimed design. The stippling in all views represent a contrast in appearance that is part of the claimed design.