On other machine (33), it will be a mess !

VPNs are generally used to allow protected access to a LAN. You could run OpenVPN on a computer and use that computer's firewall to control what can access it. What are you doing that needs to be protected from others on the LAN.

BTW, for maximum security, it's a good idea to run a firewall on all computers. That's what I do here.

so
my host which is openvpn need to be firewalled on the host itself ...whicj can be compromised and then opens the LAN

The gateway only affects things that pass through it. On the local LAN traffic passes directly between the various devices and does not go through the gateway. All you can do on the local LAN is use firewalls on the various devices or some managed switches can control what devices can talk to others.

So how can I block a specific host from specific traffic inside the lan ?

Thank you vey much

Since you're not passing through pfSense, those rules will have no effect. The rules apply to traffic between networks only and not at all on the local LAN.