i could be wrong but from what i understand in this mater is that these games mostly do all the modelling and render with softwares like Daz, Blender, or HoneySelect and the likes and use AI models to 'improve' the renders or generate sequences based in the original renders.
There are some AIs that do make 3D models but i don't believe its what you are seeking, i would recommend getting used to a 3D modelling software first, download or pirate some assets and after that you search for these AI softwares, if you want to achieve similar looks that is. I do believe the are some tutorials in the forum, luckily a better suited will user answer you.