Much of ST's offering is for nodes rather than gateways. But they do have a node+gateway pack.
Have you followed the "Tools and Software" links from https://www.st.com/en/evaluation-tools/p-nucleo-lrwan2.html#tools-software ?
I haven't followed those links. They might be commercial closed-source code / binary distributions.
I suspect Semtech keep a close handle on the gateway code to prevent abuse of their network (e.g. exceeding duty-cycles; maintaining viable commercial revenue).
