Don't worry, there's no deadline here. I'm not sure I got it so I'll try to explain what I understood. You're saying that I have to set a single IP address for the client, and allow that single address to connect to service on port 8080 on 192.168.10.1 in the firewall, right? I'm not too confident in my ability to configure the firewall, so I thought that completely isolate the subnet 192.168.2.0 and then forward a single port to it was the safe choice.
I know about Tailscale, but since it's a commercial service I'm not keen to adopt it and then maybe they stop having a free tier. I'll look into Headscale instead, I did not know about that before.
The service runs on another machine with address 192.168.1.10, so a different subnet than the WireGuard one, hence the port forward. I confirmed that this works, I can reach the service from phone on mobile data connected to WireGuard endpoint.
https://xkcd.com/979/