yeah, i tried that too, https://myurl.com:4567 renders the forum inaccessible since it doesn't return encrypted http, obviously.
Not really obviously. The URL in your config.json should be the one you're using publicly. Thus whatever your Apache reverse proxy is configured for. The configuration is used to create the URLs on your site. It has no impact on the actual communication with your reverse proxy.
My hunch is, you also need to remove that port. Because your Apache reverse proxy probably is providing your site over the standard HTTPS port. So it probably is just https://myurl.com. Also don't change anything about your reverse proxy configuration when you change this url parameter. Your reverse proxy still fetches the forum over HTTP at the port 4567. This has nothing to do with the url parameter.