Hi, I also have a similar problem despite spacedesk documents saying it can connect by USB tethering (and even direct ethernet cable?)
WIFI - Android Tablet - USB - Win10 PC - ETHERNET
In this setup: spacedesk app can detect server (possibly via router)
Since my android tablet is not a cellular model, there is no built-in USB-tethering options, there is something in developer mode with USB option "RNDIS (USB Ethernet)" but that gave no meaningful output in the first instance (or I dunno how to get it to work).
I downloaded Tetrd app, which works very well in terms of either normal tether or reverse tether, let me illustrate:
WIFI OFF - Android - USB - Win10 PC - ETHERNET (reverse tether, works!)
WIFI - Android - USB - Win10PC - unplugged (normal tether, works!)
It assigns the device an IPv4 like 10.0.3.190 and server 10.0.3.1 or .2
Works means tablet or PC has internet access.
However, neither of these options can the tablet (running app v0.9.55) detect my Win10 PC (running spacedesk server v0.9.38) even if I manualy enter those IPs. The situation that I really need it to work is :
WIFI OFF - Android - USB - Win10 PC - unplugged
I have also tried this:
WIFI OFF - Android - USB/ethernet adapter - ETHERNET - Win10 PC
I can't even get any connection to establish. It remains as unidentified network on Win10 side with no meaningful IPv4 address.
How does direct cable connection work with spacedesk? What am I missing?