There is a collision between Deep Learning Toolbox Converter for ONNX Model Format and a couple new functions added to the regular Deep Learning Toolbox in MATLAB release 2023b, specifically importNetworkFromONNX and exportONNXNetwork. There are many other issues associated with the old separate ONNX converter, so it is strongly recommended that you create a release that incorporates the built-in functions for MATLAB releases 2023b and newer.