The ornamental design for a displayscreen or portion thereof with an animatedgraphicaluserinterface, as shown and described.
FIG. 1 is a front view of a display screen or portion thereof with an animated graphical user interface showing a first image of my new design;
FIG. 2 is a second image thereof; and,
FIG. 3 is a third image thereof.
The broken lines illustrate a display screen or portion thereof, and form no part of the claimed design. 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.