I assume that you are using the internal and external networks for your login nodes. The Internal network should be interacting with the PBS Schedulers and the External network should as least have SSH port opened for users to Interact with the Login Nodes.

For Internal Network Ports Opening for PBS-Professional Clients, do take at Firewall Ports Opening for PBS-Pro Server and Clients

Make sure you put the correct Ethernet in the right zone with the right ports opening. You can take a look at how you can manipulate Linux firewall with the blog Using firewall-cmd in CentOS 7 which is applicable even for Rocky 8 which used firewalld

After unpacking, run the below client rpm only. There is no need to register the nodes with PBS Scheduler

# rpm -Uvh pbspro-client-19.2.5.20191022141354-0.el8.x86_64.rpm 

# bash