The ornamental design for a displayscreen or portion thereof including a graphicaluserinterface, as shown and described.
FIG. 1 is front view of the display screen or portion thereof including a graphical user interface showing our new design;
FIG. 2 is a front perspective view thereof; and,
FIG. 3 is an enlarged view of an icon shown on graphical user interface.
The broken line showing of a display screen including a graphical user interface is included for the purpose of illustrating portions of the article and forms no part of the claimed design.