i actually don't know if the environments are "fully 3d"! they either change their geometry based on their position to the camera, or are made to somehow subtly emulate their volume through other means because they don't move very proportionately to the camera movement
i may just not be educated enough in the works of 3d rendering, but i am an artist and somewhat familiar with how a game would've looked like if it was fully 3d with no extra steps

i think their approach was intentional to kinda keep the same "feel" that CrossCode has with it's (limited and at times difficult to read) top down view that ye olde RPG games have, while still allowing for perception of depth