Motors turn a long cable like a jumprope. The performer is wearing shoes that have wheels on them that allow them to remain upright as the rope turns under their feet, picture a knife sharpener.
The performer stands on the rope and starts to walk across the gap, two buildings for instance. As they
do, their weight changes the shape of the turning jumprope to some extent as there's a depression in the wave shape where they're pushing the rope down, for instance, when they're halfway through, there are two matching wave shapes.
This would make walking across a regular static tightrope look very boring by comparison.
The closest example I can think of is this guy "surfing" on a mechanical bull. (link)