If RustDesk works over 4G but fails on the office network, that usually points away from the PC itself and toward the local network, firewall, or internet provider.
In a recent support case, the RustDesk client connected immediately when the user switched to mobile data, but failed from the normal office connection. We first confirmed that the server details, key, relay and client configuration were correct.
We then checked the actual network connections being made by RustDesk and confirmed that the required TCP connection to the server was working. The next step was to investigate UDP traffic, which can also be important for establishing efficient peer-to-peer connections.
Because the application worked over 4G, this gave us a strong indication that the issue was network-specific rather than a fault with RustDesk itself.
This kind of comparison is useful when troubleshooting remote access problems. Testing the same device on a different connection can quickly narrow down whether the issue sits with the software, PC, local firewall, router or upstream provider.
Good troubleshooting is often about isolating the problem before changing anything.