Follow the post OpenVPN Server [Link] and create a user for the pfSense as a client of the VPN.
ADD CERTIFICATES AUTHORITY (CA)
ADD CERTIFICATE
CLIENT CONFIGURATION
ASSIGN WANVPN INTERFACE
FIREWALL RULES
Read Also
Performance OpenVPN vs WireGuard [Link]
Setting Up WireGuard VPN [Link]
OpenVPN Server + Monitoring [Link]
GRE VPN Tunnel on Cisco [Link]