Continuing the discussion from PfSense ProtonVPN Backup Connection:
Another option that I used to fix the problem where ProtonVPN connections drop out is to establish multiple ProtonVPN interfaces (I created 3), define gateways for each VPN established, group them into a gateway group, and then edit LAN rules to route traffic through the VPN gateway group. That way, if one of the VPN connection drops, there are should still be 2 others (hopefully) that are up. I will, however, check into “Service Watchdog”, as Tom suggested, to further harden my ProtonVPN connection with pfsense.