The ornamental design for a displayscreen or portion thereof with transitional graphical user interface, as shown and described.
FIG. 1 is a front view of a first image of a display screen or portion thereof with transitional graphical user interface, showing our new design;
FIG. 2 is a front view of the second image thereof;
FIG. 3 is a front view of the third image thereof;
FIG. 4 is a front view of the fourth image thereof;
FIG. 5 is a front view of the fifth image thereof; and,
FIG. 6 is a front view of the sixth image thereof.
The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-6. The process or period in which one image transitions to another forms no part of the claimed design.
The outer perimeter broken lines show a display screen or portion thereof and forms no part of the claimed design.