Problem getting https working

HI,
I've been trying to get pgAdmin 4 4.26 working with https and not having
any success. If I don't use https, it all works perfectly.

I've followed the instructions at
https://www.pgadmin.org/docs/pgadmin4/development/container_deployment.html#
and also found some info on this list in the thread
https://www.postgresql.org/message-id/1b4bba2d-910d-3017-bc5d-6b45dcac31d0%40empirica-systeme.de

I've used this config, which the same as that given in the above thread as
a known working config:
docker run -p 554:443 -v
'/etc/apache2/ssl.crt/server.crt:/certs/server.cert' -v
'/etc/apache2/ssl.key/server.key:/certs/server.key' -e
'PGADMIN_DEFAULT_EMAIL=pgadmin(at)server(dot)com' -e
'PGADMIN_DEFAULT_PASSWORD=mysecurepassword' -e 'PGADMIN_ENABLE_TLS=True' -e
'PGADMIN_SERVER_NAME=myserver.com' -d dpage/pgadmin4

The ssl cert & key are used on the host server to host run a website with
apache on ports 80 & 443 (hence the docker port 443 is re-directed to 554),
so they are valid and I've confirmed that the docker is picking them up
correctly by copying them from the running docker back to the host machine
& comparing them with the originals and they are exactly the same.

The output of docker ps is:
CONTAINER ID IMAGE COMMAND CREATED
STATUS PORTS NAMES
c2c4cc713c3a dpage/pgadmin4 "/entrypoint.sh" 17 minutes ago
Up 17 minutes 80/tcp, 0.0.0.0:554->443/tcp youthful_ptolemy

When I try to access pgAdmin in my browser using https://myserver.com:554
or https://myserverip:554 or https://127.0.0.1:554, I get this response:
Secure Connection Failed

An error occurred during a connection to intranet.threedradio.com:8443.
PR_CONNECT_RESET_ERROR

If I telnet to the server on port 554, it connects briefly and then closes
the connection, so it's definitely listening on the correct port.

I also tried redirecting port 80 to another port in case that was causing a
conflict with apache, but that didn't seem to help at all.

Hoping someone can help!

Cheers,
Ian