WiFi network without Internet but with local server

I want to have separated WiFi network for iRobot Roomba so it can not send home any data but can communicate with my Home Assistant running on RPi.

How to configure one network so devices can communicate with each other and with one specific IP adress in lan network?

Ideally if I can do it in Luci :slight_smile:

Have a look at this, you would have to add a Firewall rule that allows access to the RPi.