TechnoDadLife did a direct install video here a while back. I’m not sure if it is the same as your direct install or not chente . I couldn’t find the link on the forum but here is the YouTube link:
I've seen the video just because it's you;) I don't usually watch OMV videos and less in English :), at least this one I have been able to subtitle and translate automatically.
What you do here is install wireguard, via script, in server mode on the host to access from the outside with a point-to-site connection. You can see this configuration here. https://www.procustodibus.com/…ard-point-to-site-config/
This connection is useful to access, for example, from a smartphone to all services. This same configuration is very easy to do in a docker, I already made a guide on that, you have it here [How-To] Install Wireguard (VPN) in docker, server mode
This connection needs configurations in iptables to access other hosts within the LAN. I think that this is not convenient or much less necessary to make a backup tunnel, that is why I have proposed the guide with a point-to-point connection. This tunnel only allows packets to be routed from one host to another and only to the IP that we need to do the backup.
I tried setting up another peer on my smartphone through this same tunnel and succeeded. But to do it I had to configure rules in iptables that open more connections. It didn't seem safe to have this like this. I prefer to make independent tunnels.