sshd via socket

[David]

Folks
I'm trying a fresh install of Ubuntu 23.10, with the SSHD function 
listening to two ports via the socket method.  I'm unable to make it 
work.  There are web notes that force it to use the 'older' service 
method, but nothing about how to make the socket method work.

My trial starts immediately after install of minimal Ubuntu 23.10.  I then
  apt-get install openssh-server

Access works just fine on port 22, but now I want to ad a second 
port, let's say 2222.  I set /etc/systemd/system/ssh.socket.d/listen.conf:
   [Socket]
   ListenStream=2222

and reboot.  Port 22 works, port 2222 does not.  Where is this 
described, or what should should I be doing?