This site will generate configs for your client and server. Here is a sample config which sends only the traffic to the DVR through the VPN.
And here are the generated configs
This way there is no need to change the DVR IP when roaming. Just turn the VPN on. No third party involvement.
I see the appeal of not having a 3rd party involved -- like Tailscale. However it's probably worth noting here that if you use Tailscale with Magic DNS, there's also no need to change IPs when not on your local network. Simply use hostnames for everything. Headscale would also be an alternative for those not wanting Tailscale in the picture.
I'd have to say after a couple of years of using a mesh VPN, a point-to-point setup is starting to seem pretty quaint. Needs vary substantially of course, so for many, if all they're looking for is access from a remote streaming stick to a local media server this could be good.