Why my UE5 always access 230.0.0.1? But another computer doesn't access.

Both computers turn on the udp messaging plugin.

Welcome to the Forums, Leeettuce.
Just an idea: I remember, that I had trouble with multicast on a machine.
In my case, this was caused by VirtualBox software installed.
Disabling the Virtual Box Host Only Network in Windows Networking settings did fix the problems.