To help you find the best tool for your specific project, could you tell me: Which are the models from (e.g., GTA , ETS2 )? Which version of ZModeler was used (ZMod 1, 2, or 3)?
Available as web app, Windows/macOS desktop tool, and Python library. z3d to obj converter
Several tools and software solutions offer Z3D to OBJ conversion capabilities: To help you find the best tool for