u/Both_Trick7621

If you get the "computer is unreachable" error message on Quest 3 while using a Shadow PC, use Tailscale.

Install Tailscale on Shadow PC and the apk via F Droid on the Quest 3. Log in on both Tailscales then try to reconnect your Virtual Desktop to the Shadow PC.

It may not be a solution for you but it worked immediately for me.

I hope I can leave this post here just for others searching for a solution on Google. I spent ages trying to get it to work using VD and Shadow PC's troubleshooting methods, and other suggestions like messing around with router settings. Only found this solution hidden on a single comment on one post on Reddit.