At the moment, I have been using .FBX files for my project which is based around photorealistic representations of certain products (including shiny and transparent objects).
Is .FBX the best 3D model format to achieve Photorealism? If not, what would be the best format?
There’s a new one called USD, and the Smithsonian released a huge number of 3D assets in it. I don’t know much about it, and need to research, but look it up and see if it improves things.
The 3D format has little to nothing to do with whether something is photorealistic. Materials especially since most material features don’t convert between formats usually.