Menu "View" - "Distribute across" is available when more then two persons are selected and contains two submenu items:

Equal spaces between - frames are distributed across so that the space between their edges is made equal.

Equal center-to-centers - frames are distributed across so that distances between their centers is made equal.

The rightmost and leftmost frames stay at the same position. The example below shows how to align and distribute a group of chaotically placed frames:

Before align and distribute:

After horizontal alignment and distribution across with equal amounts of space in between frames:

The same but after horizontal alignment and distribution across with equal center-to-center distance:

See also:
Menu "Edit" - "Undo move"