Retest as-is:

root@f:~# dpkg -l openssh-server
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=================================================================
ii  openssh-server 1:8.2p1-4    amd64        secure shell (SSH) server, for secure access from remote machines
root@f:~# systemctl stop ssh
root@f:~# mv /etc/ssh/sshd_config /etc/ssh/something_else
root@f:~# cat > /etc/ssh/sshd_config <<EOF
> Include /etc/ssh/something_else
> Port 7722
> EOF
root@f:~# systemctl start ssh
root@f:~# systemctl status ssh
● ssh.service - OpenBSD Secure Shell server
     Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-06-17 11:23:58 UTC; 4s ago
       Docs: man:sshd(8)
             man:sshd_config(5)
    Process: 60797 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS)
   Main PID: 60798 (sshd)
      Tasks: 1 (limit: 38269)
     Memory: 2.6M
     CGroup: /system.slice/ssh.service
             └─60798 sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups

Jun 17 11:23:58 f systemd[1]: Starting OpenBSD Secure Shell server...
Jun 17 11:23:58 f sshd[60798]: Server listening on 0.0.0.0 port 7722.
Jun 17 11:23:58 f sshd[60798]: Server listening on :: port 7722.
Jun 17 11:23:58 f systemd[1]: Started OpenBSD Secure Shell server.
Jun 17 11:23:58 f sshd[60798]: Server listening on 0.0.0.0 port 22.
Jun 17 11:23:58 f sshd[60798]: Server listening on :: port 22.

Confirmed.

Installing from proposed:
root@f:~# apt install openssh-server
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  openssh-client openssh-sftp-server
Suggested packages:
  keychain libpam-ssh monkeysphere ssh-askpass molly-guard
The following packages will be upgraded:
  openssh-client openssh-server openssh-sftp-server
3 upgraded, 0 newly installed, 0 to remove and 38 not upgraded.
Need to get 1101 kB of archives.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 openssh-sftp-server amd64 1:8.2p1-4ubuntu0.1 [51.5 kB]
Get:2 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 openssh-server amd64 1:8.2p1-4ubuntu0.1 [377 kB]
Get:3 http://archive.ubuntu.com/ubuntu focal-proposed/main amd64 openssh-client amd64 1:8.2p1-4ubuntu0.1 [672 kB]
Fetched 1101 kB in 0s (2445 kB/s)      
Preconfiguring packages ...
(Reading database ... 55167 files and directories currently installed.)
Preparing to unpack .../openssh-sftp-server_1%3a8.2p1-4ubuntu0.1_amd64.deb ...
Unpacking openssh-sftp-server (1:8.2p1-4ubuntu0.1) over (1:8.2p1-4) ...
Preparing to unpack .../openssh-server_1%3a8.2p1-4ubuntu0.1_amd64.deb ...
Unpacking openssh-server (1:8.2p1-4ubuntu0.1) over (1:8.2p1-4) ...
Preparing to unpack .../openssh-client_1%3a8.2p1-4ubuntu0.1_amd64.deb ...
Unpacking openssh-client (1:8.2p1-4ubuntu0.1) over (1:8.2p1-4) ...
Setting up openssh-client (1:8.2p1-4ubuntu0.1) ...
Setting up openssh-sftp-server (1:8.2p1-4ubuntu0.1) ...
Setting up openssh-server (1:8.2p1-4ubuntu0.1) ...
rescue-ssh.target is a disabled or a static unit, not starting it.
Processing triggers for systemd (245.4-4ubuntu3.1) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for ufw (0.36-6) ...

Correctly picks up just the right port now

root@f:~# systemctl status ssh
● ssh.service - OpenBSD Secure Shell server
     Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-06-17 11:37:33 UTC; 25s ago
       Docs: man:sshd(8)
             man:sshd_config(5)
   Main PID: 65295 (sshd)
      Tasks: 1 (limit: 38269)
     Memory: 1.6M
     CGroup: /system.slice/ssh.service
             └─65295 sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups

Jun 17 11:37:33 f systemd[1]: Starting OpenBSD Secure Shell server...
Jun 17 11:37:33 f sshd[65295]: Server listening on 0.0.0.0 port 7722.
Jun 17 11:37:33 f sshd[65295]: Server listening on :: port 7722.
Jun 17 11:37:33 f systemd[1]: Started OpenBSD Secure Shell server.

Nothing on an unconfigured port left:

root@f:~# ss -tl | grep -e '22 '
LISTEN  0       128              0.0.0.0:7722            0.0.0.0:*              
LISTEN  0       128                 [::]:7722               [::]:*