How to setup Site to Site IPSEC VPN When Both Sites is Behind NAT (Router FTTH) - Network Protection: Firewall, NAT, QoS, & IPS - UTM Firewall - Sophos Community
Amazon.com: ExpressVPN Aircove Wi-Fi 6 Router | Dual-Band Gigabit Wireless VPN Router for Home | Built-in ExpressVPN Protection | High-Speed Coverage for All Your Devices | Easy 5-Minute Setup : Electronics
Incoming Connection to VPN-Router over Main-Router - Network and Wireless Configuration - OpenWrt Forum
Dual-router setup w/ a dedicated VPN Router: A step-by-step tutorial