The ornamental design for a displayscreen or portion thereof with transitional graphical user interface, as shown and described.
FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing my new design;
FIG. 2 is a second image thereof;
FIG. 3 is a third image thereof;
FIG. 4 is a fourth image thereof;
FIG. 5 is a fifth image thereof;
FIG. 6 is a sixth image thereof; and,
FIG. 7 is a seventh image thereof.
The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-7. The process or period in which one image transitions to another forms no part of the claimed design.
The outermost broken lines illustrate the display screen or portion thereof. The remaining broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design.