So the first thing to point out is that you will need vpn software running at both ends of your tunnel. This software should run on your PC or the local router/gateway that the PC connects to. From there the tunnel will be established over the internet, often via a 3rd Party VPN Relay Service, to the VPN software running on the Teltonika device.
With Manchester’s router hiding behind CGNAT, most people would use a VPN Relay Service, and ZeroTier is available on a RUT955 running firmware version RUT9_R_00.07.06.16.
ZeroTier has clients that will work on Windows / MacOs / Linux / Android etc. if you are going to load the VPN software on the End-User Device, to connect.
There are other options that don’t involve a 3rd party service, but as I don’t do solution design from scratch, you’re on your own, and you’ll have to do the legwork yourself. There is plenty of information out there e.g. RUT955 doesn't accept Wireguard as an option that doesn’t require a 3rd party relay service.
Once the tunnel is established you can use something like iVMS-4200, running on you PC, to point directly at the IP of your NVR, without having to port forward (assuming you are running a HikVision NVR). The only thing to watch out for is the bandwidth requirement, streaming vidio/audio over your LTE infrastrucure and link.
If you are running Hikvision NVR’s, you should be able to use Hik-Connect as an option, without having to set up a seperate VPN or have any ports forwarded.