Bigpond emails not being received on iMac macOS Ventura

Have you confirmed the credentials you used to set up the Bigpond account are correct? Mail uses the web service's data and it must be exact.

I suggest you get the proper elements for the web server, remove the local account and rebuild it per Bigpond's provided data. Generally that means an incoming mail server, an outgoing mail server, a password and a one time use setup code if required.

Some set ups such as Yahoo, have the necessary server elements embedded; all you supply is the password that allows access to web mail. If a one time access code is required, the web mail service will provide it.