So without a hotspot or internet connection, it will be very touch-and-go to maintain an offline Figma prototype. It’ll break immediately the moment someone tries to refresh the screen.
If I were stuck in this situation, I would ask the trade show folks to set up a hotspot from someone’s phone and/or rent a 5G hotspot that the touchscreen kiosks could dial into.
Otherwise, you might need to rebuild the prototype in a design tool that supports offline. Sorry that I don’t have a better answer for you here.