https://static.tp-link.com/2018/201804/20180420/1910012393_T1500_UG.pdf

At the section Example for Port Isolation, there is an example of a host that is not allowed to connect to two other hosts, but it is allowed to connect to a server. In this example I assume that an additional rule is that the two other hosts can also connect to the server.

However, the example reads

You can configure port isolation to implement the requirement. Set port 1/0/4 as the only forwarding port for port 1/0/1, thus forbidding Host A to forward packets to the other hosts.
Since communications are bidirectional, if you want Host A and the server to communicate normally, you also need to add port 1/0/1 as the forwarding port for port 1/0/4.

The last line is confusing. According to the screens the default is to allow any port to connect to any other port. Which seems to imply that the return traffic is just allowed and that no rule is necessary for communicating normally.

Instead, this rule creates the situation where only the hist and the server can communicate with each other, and the two other hosts can only communicate with each other.

Can you explain?

Sander