The solution is simple, but dangerous. The Oracle VM should ONLY be used for development and testing purposes, NEVER for a serious production system.

Now, that said, here's the solution:

Step one - turn off the firewall

In the Oracle VM, issue the following commands:

sudo systemctl stop firewalld

sudo systemctl disable firewalld

Step two - allow connections from anywhere

Edit the file: /opt/oracle/product/23ai/dbhomeFree/network/admin/listener.ora

Change localhost to 0.0.0.0

Use sudo and vim to do this.

Step three - restart the VM

That's it. It very dangerous for anything important, but this is just for dev and testing, right? Right?!