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 in a sequence of a display screen or portion thereof with transitional graphical user interface according to our design;
FIG. 2 is a front view of a second image thereof;
FIG. 3 is a front view of a third image thereof; and,
FIG. 4 is a front view of a fourth image thereof.
The appearance of the transitional image sequentially transitions between the images shown within FIGS. 1-4. The process or period in which one image transitions to another image forms no part of the claimed design.
The broken lines showing portions of the display screen and all other broken lines showing portions of the graphical user interface illustrate elements of the article and form no part of the claimed design.