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 display screen or portion thereof with transitional graphical user interface showing a first image of our new design;
FIG. 2 is a front view of a second image thereof; and,
FIG. 3 is a front view of a third image thereof.
The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another image forms no part of the claimed design.
The outermost broken line perimeter illustrates a display screen portion and forms no part of the claimed design. The remaining broken lines illustrate portions of the graphical user interface and form no part of the claimed design.