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 first embodiment of a display screen or portion thereof with transitional graphical user interface according to the claimed design;
FIG. 2 is a front view of a second image of the first embodiment according to the claimed design;
FIG. 3 is a front view of a first image of a second embodiment according to the claimed design; and,
FIG. 4 is a front view of a second image of the second embodiment according to the claimed design.
The broken lines are included for the purpose of illustrating environment and form no part of the claimed design.
The appearance of the transitional image transitions between the images shown in FIGS. 1-2 and 3-4. The process or period in which one image transitions to another forms no part of the claimed design.