I'm a bit short on time, but I think "streaming" needs to be broken down into categories of scale. Streaming video from your home Plex server (shout-out to !homelab@lemmy.ml) is a lot different than Netflix's video delivery system.
The latter intentionally stores the same content in multiple geographies, then with caches at local data centers, and sometimes even caches within your ISP's network. All of this to distribute the load of millions of users, who can just as easily be in Florida as they might be in Oregon. The duplication and redundancy means a lot of power draw, well more than just a few disks spinning up.
Whereas a home server has just one copy of the content, and since it might not always be streaming a video to you, can save power by spinning down drives or other optimizations. It is simply not possible to describe "streaming" when such radically different delivery mechanisms can all plausible be considered as streaming.
Let me make sure I understand everything correctly. You have an OpenWRT router which terminates a Wireguard tunnel, which your phone will connect to from somewhere on the Internet. When the Wireguard tunnel lands within the router in the new subnet 192.168.2 0/24, you have iptable rules that will:
So far, this seems alright. But where does the service run? Is it on your LAN subnet or the isolated 192.168.2.0/24 subnet? The diagram you included suggests that the service runs on an existing machine on your LAN, so that would imply that the router must also do address translation from the isolated subnet to your LAN subnet.
That's doable, but ideally the service would be homed onto the isolated subnet. But perhaps I misunderstood part of the configuration.