Missed the boat on the thread regarding DSM6 > DSM7 migration... so I'm just redeploying.
In DSM6 I was able to use a custom HTTPS port 8741, but that value doesn't seem to be taking in DSM7.
... I have configured the custom port and its reflected on the dashboard, but https still only listens on the default 8920 port.
Yes, I wasn't getting what you were saying because you kept saying 8920 was working inside but 8741 wasn't working outside.
On DSM 7 internally Emby will always listen on ports 8096 and 8920 and you can't change this from the UI.
It should make no difference what the SSL port is internally as you don't need to use it inside your network as you don't need things encrypted so port 8096 is fine for local use.
For remote use you can change the external/wan port to be anything your want for