I know very little about the shopping cart functionality, but I'm seeing a consistent browser console error in the Javascript:
all.min.js?v=5.1.0:9 Uncaught TypeError: Cannot read properties of undefined (reading 'split')
at Object.getPriceRange (all.min.js?v=5.1.0:9:21014)
at all.min.js?v=5.1.0:24:16259
That's almost certainly what's killing the lightbox display.
You don't seem to have any pricing options under
Tiger > Sections > Shopping cart > Pricing. I suspect you have to have something there.