Successfully using this particular router at home, primarily for its LTE connection because there is no WAN broadband internet at this location, but unable to get VPN remote access to the Synology NAS.Is it possible to disable the DrayTek routers OpenVPN Server capability.  I wish to pass-through the router and setup VPN remote-access to the OpenVPN Server installed on the NAS.This works ok at another location, using a less complicated router (BT Home Hub with port forwarding enabled) and ADSL, connecting to another Synology NAS also with OpenVPN.Not sure if the two OpenVPN servers are clashing, or whether this is possible on an LTE connection?

Does your LTE connection have a public ip address? or does your provider use CGNAT or similiar. If its CGNAT openvpn will not work unfortunately. It would work on a BT connection do its public ip address.

Many thanks Andrew, no public IP from the LTE here and its definitely some form of NAT from the mobile operator. As i have been all over the router settings, you have confirmed my suspicions that it was probably the connection. Which now also has me wondering whether it would work over Starlink?
Regards...

"3" has an APN that does (or perhaps should) provide a public IP address. It's "3internet" (no quotes).

I don't know of another mobile network that's not CGNAT.

Yes thank-you, i have also been told by another source that the mobile connection needs a SIM with a Private APN, Cheers