I am running on Windows using the v4 Service Console, but there is now a configuration option for the Runtime server port where you can set it to listen locally, public or custom.
Looking at the yaml file this creates, there seems to be an entry in the Runtime section
I suspect this is the new entry you need, although I cannot find it documented anywhere
Edit: This is the info from the Release Notes for Mendix 4.3.0 which is a slightly different format to that listed above:
When running on premise and using a reverse proxy on a different server than the application, you should enable remote access to the runtime. For this, you need to have the latest version of the Windows service console or m2ee-tools for Linux.
set runtime server port listen address to 'public' in the configuration screen of your application.
update m2ee-tools to the newest version (0.4.4) add the following configuration option to the 'm2ee' section of the m2ee.yaml configuration file: