Well, in 2D, one would expect x and y to map to camera up/down and camera left/right in some way, depending on where we decide the origin goes on the screen. In the game world, gravity might be +/- y; it’s kind of irrelevant. In any case, z has to map to the axis the camera is looking down.
But IIRC you can just apply a global transformation and use any coordinate system you like.
I haven’t used Godot, but from the info you gave, it seems like they started as a 2D game engine.
For something started as 3D, I would expect x and y to be on the floor and +z to be against gravity.
Well, in 2D, one would expect x and y to map to camera up/down and camera left/right in some way, depending on where we decide the origin goes on the screen. In the game world, gravity might be +/- y; it’s kind of irrelevant. In any case, z has to map to the axis the camera is looking down.
But IIRC you can just apply a global transformation and use any coordinate system you like.