Comment by CamperBob2

Well, they couldn't generate 2D artwork if they weren't capable of working with multiple output dimensions.

An interesting thing about transformers is that they are world-class at compressing 2D image data even when not trained on anything but textual language ( https://arxiv.org/abs/2309.10668 ). Whether that notion is relevant for 3D content would be two or three figures over my pay grade, though.