@plypo Since your doing this rfc1918 to rfc1918 you could do it without a port forward because you don't need a nat. But you would need to create a route on the 192.168 device.
And then allow the traffic just on the wan interface via a rule, no nat or port forward needed.
And you would have to setup a no nat outbound rule so that when devices on your 10 network are talking to your 192. network they don't nat..
I would never in a million years set it up like this.. I would turn your isp device into just a modem, turn off its wifi and get a real AP for my local wifi. And put everything behind pfsense. Worse case just turn off wifi on your isp device and just double nat, etc.
But there are few different ways to skin this cat. One being your typical port forward scenario, the other is just setting up routes on your devices in 192.168 to point to pfsense wan IP to get to the 10 network. And allowing via wan firewall rules, and disable nat outbound on pfsense when talking to anything other than your 192.168.1.1 gateway.