Some advanced users flash or Padavan onto the TL-WDR7660. This completely changes the OS and may add VPN client support. However, the TL-WDR7660 has a Mediatek chipset that is poorly supported. You risk bricking the router.

Use a or an old PC with SoftEther (supports L2TP/OpenVPN) behind the router, then forward ports.

On a Windows/macOS/Android device → Add VPN connection → Server = your DDNS hostname → Use the account created.

Connect a VPN-capable router (e.g., a GL.iNet travel router or a PC with pfSense) to the WAN port of the TL-WDR7660. Then connect all devices to that secondary router.