Display Screen or Portion Thereof with a Mixed Reality Graphical User Interface

FIG. 1 is a front view of a first image for a display screen or portion thereof with a mixed reality graphical user interface showing a first embodiment of the 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 of the graphical user interface 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 long dashed double-short dashed broken lines in FIGS. 1 to 3 show the field of view for the display screen or portion thereof, and form no part of the claimed design. The remaining broken lines illustrate the graphical user interface or a mixed reality environment, and form no part of the claimed design.