I have successfully set up port forwarding for UDP 4500, 500 and 1701 to a Windows 2012 server and the VPN works fine.
Changing the target node to a Win 2019 server the VPN fails although the server configuration is identical in both cases. Internal connections to the 2019 VPN work perfectly.
Using Wireshark I note that the BT Hub doesn't appear to be routing any packets to the 2019 server.
Anyone any ideas?
Home hubs are easily confused. Try a factory reset and try again