Assetto Corsa Connection Issue The Server Seems To Be Unavailable Fix Link

Some ISPs use "Carrier Grade NAT" (CGNAT), which breaks AC entirely. You cannot port forward CGNAT.

Reset network-related game settings:

Try a different network (mobile hotspot) to confirm whether your home network is the issue.
Ask other players whether they can join the same server (helps isolate server vs. client).
Reinstall the game or create a fresh Windows user profile and test.