What is claimed is the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described.
FIG. 1 is a first image in a sequence showing a display screen or portion thereof with a graphical user interface for a checkpoint validation system; and,
FIG. 2 is a second image in a sequence showing a display screen or portion thereof with a graphical user interface for a checkpoint validation system.
The outermost broken lines in the drawings show a display screen or portion thereof and forms no part of the claimed design.
The other broken lines in the figures show portions of the graphical user interface that form no part of the claimed design.
The appearance of the transitional image of the graphical user interface transitions between the images shown in FIG. 1 and FIG. 2. The process by which one image transitions to another forms no part of the claimed design. The period in which one image transitions to another forms no part of the claimed design.