Defining WEB_UI Port & Listening Port as same port - incorrect?

[RadTunesly]

I've just started out using containers, in the process of setting up a Synology NAS using https://trash-guides.info/File-and-Fold ... /Synology/ and their hotio qbittorrent image using port 8088. This is routing through a NordVPN Wireguard container.

After some hassle setting up Nordlynx I've gotten this working and tested it using https://torguard.net/checkmytorrentipaddress.php and it's working successfully. Then I went through and updated the recommended setting for qbittorrent via the Web UI and changed the setting:
Options > Connection > Listening Port > Port used for incoming connections : from 50000 to 8088

When I run the Torguard torrent IP address check again it's no longer registering my VPN output address, it's not finding anything at all. Changing it back to 50000 works, showing my VPN address again.

I'm pretty sure there is a gap in my understanding as I'm new to home networking and opening ports. The Trash Guide recommends setting the listening port to "The port you opened in your router/firewall or port forwarded at your VPN provider".
Isn't the port I specified in the docker-compose (8088) the one I should be listening on?

Hoping someone can close my clear knowledge gap.