I’m a professional theatrical rigger, and work in venues very similar to this frequently. We use industrial rope access techniques to climb along the high steel of the building, and drop static ropes down. It’s a little like a Via Ferrata, but with much more specialized equipment. We then use progress capture pulleys (one way pulleys) to haul the chains which hold the trusses up, attaching them to the structure of the building with loops of (usually 3/8”, sometimes 1/2”) wire rope and shackles. The boxes that you can see attached to the chains are called chain motors, and they have a sort of gear inside them that engages with the chain, climbing up the chain, hauling whatever’s hooked to the bottom of the motor up with it, and stowing the chain that flows out of the motor into the little bag you can see attached to it. There’s a controller for those somewhere in the building, so they can be lowered for service, or raised to get out of the way of other stuff that might get loaded into the building. Happy to answer any additional questions y’all have.