Ethernet connection overrides wifi for internet access, despite no device blocking and "only resources of its network" setting

Question

I have found various other questions relating to this issue but none of the solutions worked in my case. This is all using a fresh installation of Ubuntu 20.04.01 LTS on a new Dell optiplex. The wireless card is a USB connected TP-LINK TL-WDN3200.

I am connecting two machines directly with an ethernet cable, and both independently via WLAN cards to a router (and to the internet). The ethernet connection works fine, but the moment I activate the wired connection in network settings, all traffic is routed through this connection, despite there being an active WLAN connection. The WLAN appears to work (I can still see available networked), and it does not appear as blocked with rfkill list all. I am manually setting the IPs of both machines, with no gateway IP, and have tried various settings, specifically "Use this connection only for resources of its network", disabling IPv6, and using "Link-Local Only". None of these resolve the issue, and traffic is routed through the ethernet link the moment it is connected until it is turned off.

Answer 1

Resolved this. I was setting the IP manually as 10.0.0.10, but this automatically routed 10.0.0.0 IPs to the ethernet connection, where it was supposed to go to the wifi router. Changing the IP to 11.0.0.10 resolved the issue.