Hi

I bought a router DECO BE65-5G for a remote site behind a CGNAT IP, typical setup nowadays for a 5G connection

on the central site I run a TP LINK MR600  with public IP and DDNSand  with openVPN server enabled, how can I connect the Client from the DECO BE65 to the server from  the MR600 and enable site-to site connectivity, ie remote and central subnets can talk to eah others thru the VPN ? 

Note that I can connect from a PC or IPhone to the central site MR600 Server through OPENVPN, it works pretty well I can reach all devices on the central site LAN from my Iphone

feasible with OPENVPN ?

 then what do I miss ?

or any other type of VPN that could be used  ? 

 PPTP  ?

L2TP/IPSEC ? 

thanks

Damien