The ornamental design for display screen or portion thereof with icon, as shown and described.
The FIGURE is a front view of a display screen or portion thereof with icon showing our new design.
The outermost broken lines illustrate an electronic device, which is the environment of the design, and form no part of the claim. The remaining broken lines illustrate a display screen or portion thereof and portions of the graphical user interface, and form no part of the claimed design.