thank you once again; I've made it.
I deleted all my previous configs and started again. The problem was declaring the VPN tunnel on my pfsense client configuration. Since the server has been set to dynamically provide IP addresses through the VPN tunnel, I think it conflicted somehow.
Just for anybody else facing this issue, I've managed it in this way:
SERVER SIDE:
Schermata 2023-01-04 alle 12.17.36.jpg
(note the dynamic IP address network)
then I declare the subnet to which all clients should be given access (I previously named this subnet LAN B)
Then, on specific USER PERMISSION (OPENVPN ACCESS SERVER) I set:
Schermata 2023-01-04 alle 12.21.28.png
So that the user I'm connecting from will be capable of reaching both my client side LANS (the pfsense's ones)
CLIENT SIDE (pfsense)
No tunnel ip has been declared (because it is dynamically provided by the server)
Schermata 2023-01-04 alle 12.23.45.png
The remote LAN I want to reach has instead been declared (192.168.1.0/24 - SERVER SIDE LAN)
NO GATEWAY NOR STATIC ROUTE HAS BEEN MANUALLY SET; THEY GOT CREATED BY OPENVPN CLIENT ITSELF
Schermata 2023-01-04 alle 12.26.02.png
Everything's working now: I can ping the external LAN (server side - 192.168.1.0/24) from both my pfsense LANs (192.168.3.0/24 and 192.168.4.0/24).
Thank you once again!