I understand that you wish to reproduce plots for Down Link Simulation using the MATLAB '5G New Radio Polar coding' example while using native MATLAB instead of C.
You can utilize the '5G Toolbox' and refer to the following Mathworks documentations which specify MATLAB examples to achieve the desired result.
'5G New Radio Polar coding': https://www.mathworks.com/help/releases/R2022a/5g/gs/polar-coding.html?searchHighlight=5g%20new%20radio%20polar%20coding&s_tid=doc_srchtitle
'Downlink Channels': https://www.mathworks.com/help/releases/R2022a/5g/downlink-channels.html?searchHighlight=downlink%20channels&s_tid=doc_srchtitle
Hope this helps! Thanks.